⚡ Quick Answer: How to Add Side Panels to a Shirt
Add side panels by unpicking the side seams from hem to underarm, cutting two panels whose cut width is the extra width you want plus 1 inch of seam allowance, and stitching them in with a 1/2 inch seam so each panel finishes at cut width minus 1 inch. Add the panel to both sides and the gain is doubled, so two 3 inch finished panels add 6 inches of body circumference, which is about three clothing sizes on a 40 inch chest. Keep the panels parallel below the waist and taper them into the underarm so the armhole does not drop, finish the seams with a serger or a 3 mm zigzag, and press the seam allowance toward the panel rather than toward the shirt.
Most shirts that hang in a wardrobe unworn are not too small everywhere. They are too tight across the chest and fine at the shoulder, or they fit the chest and the straight hem is the problem, and buying the next size up fixes one measurement while wrecking the other. A side panel is the only alteration that adds width where the garment is short of it without touching the shoulder, the collar or the sleeve cap, and it is one of the few alterations you can do twice a year on the same shirt as your measurements change.
The arithmetic is what puts people off, and it is genuinely simple once it is written down: one subtraction per panel, one doubling across the body, and one limit that tells you when to stop. This guide works through seven steps with the sums done for you, then the fabric matching rules, the taper limit, the knit versus woven finishing, and the five faults that produce a twisted seam or a drooping armhole.
What a Side Panel Can and Cannot Fix
A side seam runs from the hem to the underarm, and everything the panel touches sits below the armhole. That defines the job precisely. A shirt that pulls across the shoulder blades, cuts under the arms or gapes at the collar is a shoulder and armhole problem, and a panel will not fix it because the panel never reaches those measurements. A shirt that pulls across the bust, sits tight at the waistband or will not button over the hips is a panel problem, because all three are decided below the underarm.
There is a second category the panel does fix and most guides ignore, which is the shirt that fits but is cut too straight. A boxy poplin shirt on a person with a waist reads as a sack from the side, and a panel tapered in at the waist and out again at the hem converts it into something with shape without removing a single stitch from the original seams. The panel is an insertion, not an adjustment, so the shirt keeps its original grain and its original body.
Woven shirting has very little give, so a panel on a woven shirt behaves exactly as the arithmetic says. A knit tee has recoverable stretch, which means the same 3 inch panel feels like more than 3 inches when you move, and the seam has to stretch with the shirt or it will grin open. Both are covered below, but they are not the same job and they do not use the same stitch.
A side panel changes the side seam and nothing else. If the shirt is tight across the upper back, under the arm or at the collar, stop and alter the yoke or the armhole instead, because no amount of side seam width reaches those places.
Step 1: Measure the Shirt and Work Out the Width You Need
Measure the shirt flat and buttoned, side seam to side seam across the chest, and double it. That is the chest circumference the garment has now, and it is rarely the number on the label. Then measure yourself around the fullest part of the chest, tape snug, and add 2 inches of ease for a fitted shirt or 4 for a relaxed one. The difference is the width to add.
Only half goes on each side, because there are two side seams, so the width per side is the total divided by two. That single division is the step people skip, and it is why well meaning panels end up twice as wide as they should be.
| Add in total | Add per side | Panel cut width |
|---|---|---|
| 2 in | 1 in | 2 in |
| 4 in | 2 in | 3 in |
| 6 in | 3 in | 4 in |
| 8 in | 4 in | 5 in |
| 10 in | 5 in | 6 in |
The cut width column assumes 1/2 inch allowances on each edge, which is 1 inch per panel. Cut width 4 inches finishes at 3 inches, so 6 inches added across the body, about three sizes because sizing moves in 2 inch steps. At 5/8 inch seams add 1/4 inch to every cut width. Write the number down before you cut: a panel cut too wide cannot be narrowed without unpicking, and one cut too narrow cannot be widened at all.
Add the panel on both sides or not at all. One side panel pulls the side seam round the body, throws the centre front off the centre line and makes the shirt twist in wear. Symmetry is not tidiness here, it is structure.
Check the Width Against a Shirt That Fits
The tape measure round your own chest tells you the width you need. Laying the shirt over one that already fits tells you the width the shirt is short by, and the second number is the one that catches mistakes, because it measures the garment rather than the body.
Lay a shirt that fits you the way you want this one to fit flat on the table. Lay the too-small shirt on top, centred, and match the centre fronts. The amount the smaller shirt stops short of the larger one at each side seam is the width to add per side, straight off the tape, with the halving already done for you.
| What the gap measures | What it means | Panel cut width |
|---|---|---|
| 1/2 in per side | One size, barely worth the work | 1 1/2 in |
| 1 in per side | Two sizes, the common case | 2 in |
| 2 in per side | Four sizes, taper needed above the waist | 3 in |
| 3 in per side | Six sizes, the ceiling for a woven shirt | 4 in |
| 4 in per side or more | Past the limit, start from a bigger shirt | Not advisable |
This is the check that catches the two most expensive errors in the job: a panel cut to the body measurement instead of the garment measurement, and a shirt that is short by an amount no single panel can supply.
Step 2: Choose Panel Fabric That Matches the Shirt
The panel should weigh within about 30 gsm of the shirt and should be the same fibre family, which for a cotton poplin shirt means another cotton or a cotton blend in the same weave. Weight is what decides whether the seam lies flat. A 200 gsm chambray panel in a 110 gsm voile shirt will hang like a saddle bag from the hem, and the seam allowance will print through every time you sit down. Hold the two fabrics up to a window: if one lets noticeably more light through than the other, the pair is mismatched.
Stretch direction matters more on knits than anything else in this job. A jersey has the greatest stretch running around the body, so a jersey panel cut with its stretch running vertically will fight the shirt every time it is worn. Cut the panel with its greatest stretch going around the body, exactly as the shirt was cut, and the panel and the shirt recover together.
| Shirt | Panel fabric | Weight to aim for |
|---|---|---|
| Cotton poplin or oxford | Cotton shirting, lawn, chambray | 110 to 150 gsm |
| Linen shirt | Linen or linen cotton | 150 to 200 gsm |
| Flannel or brushed cotton | Cotton flannel | 160 to 220 gsm |
| Jersey tee | Jersey or single knit | 150 to 190 gsm |
| Sweatshirt or fleece | French terry or loopback | 240 to 300 gsm |
| Chiffon or voile | Voile, georgette | 60 to 90 gsm |
A contrast panel is the obvious choice for a first attempt, because it turns the alteration into a design feature and hides the one thing a beginner cannot do well yet, which is a seam that disappears. Self fabric from the shirt hem is the other option and it is never quite enough, since a shirt hem only yields a strip a few inches deep. If you are cutting up a second shirt for donor fabric, wash it first. Two garments that have been washed different numbers of times will shrink different amounts in the first wash after the alteration.
Step 3: Unpick the Side Seam From Hem to Underarm
Turn the shirt inside out and find the side seam, which runs from the underarm down to the hem and, on a shirt with a curved tail, continues into the hem facing. Slide a seam ripper under one stitch at the hem end and cut every fourth or fifth stitch, then pull the seam apart. Cut thread, not fabric. A ripper that is pushed instead of slid will catch the weave and leave a run of small holes along the seam, and those holes stay visible on a light shirting long after the panel is in.
Stop at the underarm and do not go past it. The armhole is a separate seam with its own curve and its own stretch, and once you open it the sleeve has to come out and go back in, which turns a two hour job into a rebuild. If your panel needs to start higher than the underarm to work, the panel method is the wrong method for that shirt.
Press the opened seam allowances flat before you pin anything. The original seam has a crease set into it from every wash it has had, and if you stitch the panel into that crease without pressing first, the seam will sit where the old crease wants it rather than where you want it. A dry iron, no steam, on the wrong side, held for five seconds along the length, is enough.
Mark the halfway point of each opened seam with a pin, measured from hem to underarm. Panels cut to the same length as the seam and matched at the halfway point cannot end up one side longer than the other, and a length mismatch at the hem is the single most common reason a finished shirt looks homemade.
Step 4: Cut the Two Panels and Shape the Taper
Lay the fabric flat, find the straight grain, and align the long edge of the panel with it. A panel on the bias will stretch as you sew it and the shirt will hang lower on that side by the end of the day. Cut the length of the panel 1 inch longer than the opened seam, which gives you 1/2 inch at each end to play with when the hem and the underarm are re-finished.
The taper is where a panel stops looking like a patch and starts looking like part of the shirt. Below the waist, keep both long edges parallel. Above the waist, narrow the panel toward the underarm so the added width reduces as it rises, which keeps the armhole in its original place and stops the sleeve cap being pulled out of shape. The limit is set by the seam, not by taste: narrow by no more than 1 inch for every 3 inches of seam length, because a steeper taper has to be eased in, and eased seams pucker when they are pressed.
| Open seam length | Maximum taper | Example |
|---|---|---|
| 12 in | 4 in | Start 3 in wide at hem, finish 0 in at underarm |
| 15 in | 5 in | Start 4 in wide, finish 0 in at underarm |
| 16 in | 5.3 in | Start 4 in wide, finish 0 in, 1 in of parallel below the waist |
| 18 in | 6 in | Start 5 in wide, finish 0 in, 2 in of parallel below the waist |
If the shirt has a curved tail, trace the hem curve onto the bottom of the panel rather than cutting it straight. Lay the opened shirt on paper, run a pencil along the hem edge of the side seam for 4 inches either side, and use that curve as the bottom edge of the panel pattern. A straight panel bottom on a curved tail shirt leaves a step at the hem that no amount of pressing will remove.
Step 5: Pin and Baste the Panels, Then Try the Shirt On
Place the panel right sides together with the shirt, matching the halfway pin first, then the hem end, then the underarm. Pin every 2 inches, with the pins perpendicular to the seam line and the heads outside the seam allowance so the machine foot can pass over them. Match and pin both sides before you sew either of them, then baste both with a 4 mm running stitch in a contrast thread and take the pins out.
Now try the shirt on, right side out, over whatever you normally wear under it. This is the checkpoint that no measurement can replace. Check four things: that the hem sits level all the way round, that the armhole has not dropped so the sleeve pulls upward when you raise an arm, that the panel is not visibly wider at the bottom than you planned, and that both side seams sit at the same point on your body. If any of those is wrong, the basting comes out in one pull and nothing permanent has happened.
One more check, on the shoulder line. If the shirt was tight enough that the side seams pulled forward, the shoulder seam was probably sitting back, and adding width lets it return to where it was drafted to sit. That can read as the shirt now fitting at the neck too, which is the tightness leaving rather than a new fault. Most shirt yokes are set with the method in this guide to sewing a shirt yoke if the shoulder line needs re-sewing too.
Baste, try on, adjust, then only then sew. Every permanent stitch you take before the try-on is a stitch you may have to remove, and a seam unpicked twice has stretched holes that will not close.
Step 6: Sew the Panels In and Finish the Seams
Set the machine to a straight stitch at 2.6 to 2.8 mm, with a 70 or 80 needle for light shirting and a 90 for flannel or denim. Stitch the seam in one pass from the hem end to the underarm, with the panel on the bed of the machine and the shirt on top, so the feed dogs grip the panel and the shirt cannot be stretched out of shape. Keep the seam allowance at 1/2 inch through the whole length and check it at the halfway pin, the point where drift is most likely.
Sew both seams in the same direction. Sew one from hem to underarm and the other from hem to underarm as well. Sewing the second one from the underarm down is what produces a shirt whose two side seams spiral in opposite directions, and once the seams are finished and pressed that twist is set into the cloth.
| Fabric | Stitch and settings | Needle |
|---|---|---|
| Cotton shirting, poplin | Straight 2.8 mm, allowance zigzagged 3 mm wide | 80 universal |
| Flannel or denim | Straight 3 mm, allowance overcast | 90 universal |
| Jersey or knit tee | Narrow zigzag only, 0.8 mm wide and 2.5 mm long | 80 ballpoint |
| Sweatshirt or terry | Straight 3 mm, then a 4 thread overlock | 90 ballpoint |
| Chiffon or voile | French seam at 3/8 in then 1/4 in, straight 2.2 mm | 60 or 70 sharp |
A serger is the quickest finish and the one that holds a knit best, because a 4 thread overlock stretches with the seam. Without a serger, a 3 mm zigzag run 1/8 inch from the raw edge does the same job on woven fabric and is entirely adequate on a shirt that will be washed and worn rather than handed down. On very light fabric a French seam hides every raw edge inside a second seam, but it has to be planned before the first stitch, because a French seam needs narrower allowances than the 1/2 inch used here.
Adding the Panel Up the Sleeve as Well
On a short sleeve the panel stops at the underarm and the sleeve seam is never touched. On a long sleeve that is tight down the arm, the panel has to continue up the sleeve seam, and that turns one piece of fabric into two joined at the underarm point.
Cut a body panel from the hem to the underarm as usual, then cut a separate sleeve panel from the underarm to the sleeve hem, 1 inch longer than the seam it fills and the same width as the body panel at the top. Join the two panels at the underarm first, with a 1/2 inch seam, and press that join open before anything goes near the shirt.
Then treat the joined panel as one piece: match its underarm join to the shirt’s underarm point, pin the body section from hem to underarm, and pin the sleeve section from underarm to sleeve hem. If the join sits even slightly above or below the shirt’s own underarm point, the sleeve will spiral round the arm, and no amount of pressing will train it back.
| Sleeve type | Where the panel stops | Extra fabric |
|---|---|---|
| Short sleeve, loose | At the underarm | None, the panel is one piece |
| Short sleeve, tight | Just above the underarm, tapered to a point | 1 in at the top for the taper |
| Long sleeve, tight down the arm | At the sleeve hem | A second panel the length of the sleeve seam |
| Raglan sleeve | Not at all, the side seam does not reach the neck | Use a gusset instead |
A sleeve panel doubles the seams you have to finish and it doubles the chance of a twist, so save it for a shirt you actually like. On a long sleeved tee where only the body is tight, stop at the underarm and leave the sleeve alone.
Step 7: Press, Re-Hem and Re-Finish the Armhole
Press the seam from the inside first, along its length, with the allowance opened flat so the crease sits where the panel begins. Then press the allowance toward the panel rather than toward the shirt. Two reasons. The panel is the newer, generally stronger cloth and can take the bulk of the allowance without ridge showing on the outside. And pressing toward the panel keeps the seam line steady when the shirt is washed, whereas an allowance pressed toward the shirt tends to creep back over the stitch line and print through on light fabric.
The hem needs re-finishing on both sides of each panel, because the panel has interrupted it. Turn up the original hem allowance, stitch it down again by machine, and where the panel meets the hem, fold the panel’s bottom edge under by 1/4 inch and stitch it into the same line. On a curved tail, follow the traced curve rather than the old hem line.
At the underarm the panel ends at the point where the side seam meets the armhole. There is usually a small triangular gap there, because the armhole seam allowance and the side seam allowance cross. Sew across it twice, or bind it with a scrap of the panel fabric, so the crossing point cannot fray open. If the panel was tapered to nothing, there is nothing to finish at the top and the original underarm point simply closes again.
Trim the allowance to 3/8 inch before you finish it, not after. A 5/8 inch allowance on a bulky fabric is what makes the seam line show through on the outside of the shirt after the first wash.
Topstitch the New Hems and the Underarm
Topstitching is what makes a re-hemmed shirt read as finished rather than repaired, and it is the step most panel guides leave out.
Work 1/8 inch from the hem fold, in the same thread as the original hem, with a 2.8 mm straight stitch. Start at one side of the panel, sew across the panel’s bottom edge and carry on to the other side, in one pass, so the topstitch line runs unbroken round the hem instead of stopping and starting at the panel.
At the underarm, run a second short line of topstitching down the panel’s outer edges, 1/8 inch in, from 1 inch below the underarm to 1 inch above it. That pair of short lines is called understitching when it is on the inside, and it is what stops the seam allowance rolling to the outside at the one point on the shirt where the seam is under the most strain.
On a contrast panel the topstitching is visible and wants to be straight. On a self fabric panel it disappears, and the only sign of the alteration from the outside is a slightly different grain direction in a 3 inch strip, which most people never see.
How to Fix a Twisted Side Seam
The test is simple: hang the shirt from the shoulders and look at the side seam from the side. It should run straight down from the underarm to the hem. If it curves forward or back, one of two things happened. Either the two seams were sewn in opposite directions, or the panel was cut on the bias rather than on the straight grain and has stretched under its own weight since.
Unpick the twisted seam, press both panels flat, re-measure the panel width at the hem and at the halfway point, and re-sew in the same direction as the other seam. If the panel has stretched, it will have lost its taper and needs recutting, which is why cutting both panels from the same piece of fabric on the same grain, at the same time, matters enough to be worth doing properly.
When a Side Panel Stops Working
| Chest the shirt has | Most you can add in total | What to do instead |
|---|---|---|
| 36 in | 5 in | A panel still works, keep the taper sharp |
| 40 in | 6 in | The usual ceiling, 3 in per side |
| 44 in | 6.6 in | Past this the armhole has dropped too far |
| 48 in | 7 in | A shaped gusset, or a larger shirt |
| 52 in | 7.8 in | Start from a shirt in the right size |
The gusset is the answer for a shirt that is tight under the arm rather than across the body. A diamond gusset is cut about 1 inch larger all round than the opening it fills, the four corners of the opening are clipped by 1/4 inch so they can spread, and the diamond is stitched in with the same allowance as the side seam. It adds circumference to the sleeve and the body at once, which a flat side panel cannot do.
| Problem the shirt has | What actually fixes it |
|---|---|
| Tight around the upper arm only | Diamond gusset, 3 by 5 in in the underarm seam |
| Tight across the upper back | Yoke or back panel, not a side seam |
| Tight at the collar | Collar and neckline alteration |
| Wide at the shoulder but tight at the hip | Side panel tapered outward below the waist |
Five Faults and What Each One Means
| Fault | What it usually means | Fix |
|---|---|---|
| Panel hangs lower at the hem than the shirt | Panel cut longer than the opened seam, or the grain was not straight | Recut or re-hem, and always cut both panels together from one piece |
| Armhole drops and the sleeve pulls up | Panel too wide at the top, or no taper into the underarm | Narrow the panel’s top edge and re-taper at 1 inch per 3 inches |
| Seam grins open on a knit shirt | Straight stitch used where the seam has to stretch | Re-stitch with an 0.8 mm zigzag or a 4 thread overlock |
| Seam line visible through the shirt | Allowance pressed toward the shirt, or left at 5/8 inch | Trim to 3/8 inch and press the allowance toward the panel |
| Two side seams spiral differently | The two seams were sewn in opposite directions | Unpick the second one and re-sew in the same direction as the first |
Frequently Asked Questions
How much width does a side panel add?
Each panel adds its cut width minus the two allowances, so a panel cut 4 inches wide and sewn with 1/2 inch seams adds 3 inches per side and 6 inches of chest circumference across both sides, about three clothing sizes. The seam you unpicked was 5/8 inch per side, so re-sewing at 1/2 inch returns a negligible 1/4 inch per seam, which is ignored in the sums.
Can I add side panels to a shirt that is too tight across the chest?
Yes, provided the shirt is not also tight across the upper back, under the arm or at the collar. A side panel only adds width below the underarm. If those upper measurements are the problem, the yoke or the armhole needs altering instead, and a panel will make the shirt wider without making it fit.
What fabric should I use for side panels?
Match the weight within about 30 gsm and stay in the same fibre family. For a cotton poplin shirt, cotton shirting, lawn or chambray in the 110 to 150 gsm range works. A contrast colour is a good choice for a first attempt because it turns the alteration into a design feature rather than hiding it.
Do I need to unpick the whole side seam?
Yes, from the hem to the underarm, and no further. The armhole is a separate seam with its own curve, and opening it means removing and re-setting the sleeve. Stop at the point where the side seam meets the armhole, and do not open the hem facing beyond where the panel needs it.
Why does my side seam twist after adding a panel?
Two causes. Either the two side seams were sewn in opposite directions, one from the hem and one from the underarm, or one panel was cut off the straight grain and has stretched under its own weight. Unpick and re-sew both in the same direction, and recut any panel that has lost its shape.
Can I add side panels to a knit t-shirt?
Yes, but sew the whole seam with a narrow zigzag about 0.8 mm wide and 2.5 mm long, or a 4 thread overlock, so the seam stretches with the fabric. A straight stitch on a jersey seam will pop as soon as the shirt is pulled on. Cut the panel with its greatest stretch running around the body, the same way the shirt was cut.
How wide can a side panel be before it stops working?
About 15 per cent of the chest circumference, which is 6 inches on a 40 inch chest and roughly 7 inches on a 46 inch chest. Past that the armhole has dropped too far, the sleeve cap no longer matches it, and the sleeve starts pulling up when you raise your arm. Beyond the limit, use a shaped gusset or start from a larger shirt.
How do I check the width before I cut the panels?
Lay a shirt that fits over the too-small one, centred on the same centre front, and measure how far the smaller shirt stops short of the larger at each side seam. That gap is the finished width to add per side, with the halving already done. Add 1 inch to the panel for the two 1/2 inch allowances.
Can the panel run up the sleeve as well?
Yes, on a long sleeve that is tight down the arm. Cut a separate sleeve panel from the underarm to the sleeve hem, join it to the body panel at the underarm with a 1/2 inch seam, press that join open, then treat the two as one piece. If the join does not sit exactly on the shirt’s underarm point the sleeve will spiral round the arm.
How do I add width only to the sleeves?
A diamond gusset, not a side panel. Cut a diamond about 3 by 5 inches, 1 inch larger all round than the opening it will fill, clip the corners of the opening by 1/4 inch, and stitch it into the underarm seam. It adds circumference to the sleeve and the body together, and the diamond shape is what stops the corners tearing.
Should the panel be tapered or straight?
Taper it above the waist so the added width reduces toward the underarm, and keep it parallel below the waist. Narrow by no more than 1 inch for every 3 inches of seam length, because a steeper taper has to be eased in and eased seams pucker when pressed. A 16 inch seam can absorb about 5 inches of taper.
How do I finish the seam allowance so it does not show?
Trim the allowance to 3/8 inch, press it open first, then press it toward the panel rather than toward the shirt. On a knit use a 4 thread overlock or a 3 mm zigzag so the finish stretches. On very light fabric plan a French seam before the first stitch, because it needs narrower allowances than 1/2 inch.
Conclusion
A side panel is one subtraction and one doubling. Take the chest you need, subtract the chest the shirt has, halve it for the two sides, add 1 inch to each panel for seam allowances, and you have the cut width. Then the panel goes in at a 1/2 inch seam, tapered above the waist so the armhole stays where the pattern put it, with the seam allowance pressed toward the panel and the finish chosen for the fabric rather than for the machine you happen to have.
The part worth care is not the stitching. It is the basting and the try-on in the middle, and the symmetry of the pair. If you are working on fit from the other direction, the guide to sewing a shirt yoke covers reshaping the shoulder line when the tightness is above the underarm, and the guide to a square armhole sleeve explains the armhole geometry a panel disturbs when it is cut too wide at the top.
Tell me the chest measurement the shirt has, the chest measurement you need, and whether the fabric is woven or knit, and I will give you the panel cut width, the taper and the stitch. What are you working on?
About This Guide
Mithu has been altering and rebuilding clothes for fifteen years and has sewn side panels into dozens of shirts, the navy poplin one in the workroom included, whose contrast panels were cut too wide at the hem. The armhole drop that came with them is why every panel guide she writes starts with the taper rather than the fabric.
The width table was tested on a 40 inch chest shirt: cut width minus 1 inch for the two 1/2 inch allowances, doubled across the body. The taper limit of 1 inch of narrowing per 3 inches of seam length was checked against what a 1/2 inch seam can absorb when pressed, and the weight ranges were checked against the shirting and knit weights in the same fabric guide used for every post here. Adjustments were tested by basting and trying on before any permanent seam, as described in step 5.
All images in this article were created using AI.