⚡ Quick Answer: How to Sew Granny Squares Together
Lay the squares side by side, right side up, matching stitch to stitch, and work a mattress stitch through the back loops only for a seam you cannot see from the front, or a whip stitch through the same loops if you want speed. Join the squares into strips first and join the strips second, and work every seam in the same direction. A 5 in square joined this way adds about 1/8 in, so ten squares across give you a little over 50 in, not 50.
Two crocheted squares are easy. The blanket is where it goes wrong, and it always goes wrong in the same three places: the squares were never measured, the seam was pulled tight stitch by stitch, and the joins were worked in whatever order the maker felt like that evening. Each of those leaves a mark you can see from across a room, and all three are settled before you thread a needle.
This guide joins the two ideas that most crochet tutorials keep apart. It gives you the seven seams worth knowing and the one number for each of them, then it gives you the working order that keeps a blanket flat and square while you sew it. If the squares themselves are the problem rather than the seam, start with how to sew a blanket without a sewing machine for the no-sew side of the same question.
Step 1: Measure One Square Before You Sew Anything
A granny square is not a fixed size. In worsted weight yarn on a 5 mm hook, three rounds lands anywhere between 3 1/2 in and 4 3/4 in depending on how you hold the hook, and each extra round adds roughly 1 1/2 in. That spread is fine for a single square and ruinous across a blanket, because a quarter inch of drift on every square becomes 2 1/2 in across ten of them.
So block first, then measure. Lay five finished squares flat, measure the same edge on each, and write the average down. Multiply it by the number of squares you plan to use across: a 5 in square, ten across, is 50 in before any seam and about 51 in after them. If the average comes out at 4.75 in instead, that same blanket is 48 in, which is the difference between a throw and a cot blanket. Square count follows from the same number, and it is worth settling before you crochet 300 more of them:
- A baby blanket at 30 x 36 in takes 42 squares at 5 in, which is a 6 by 7 grid.
- A throw at 48 x 60 in takes 120 squares at 5 in, which is 10 by 12.
- The same throw at 6 in squares takes 80, which is 8 by 10, and 40 fewer seams to sew.
Yarn to match: a 6 in granny square in worsted weight eats about 32 yd, so 120 five inch squares is roughly 2,000 yd of yarn before you add the joining colour and a border. Buy the joining colour first, all in one dye lot, because running out halfway through the last strip is the most common way a blanket stalls for a year.
Step 2: Choose the Seam by What the Blanket Has to Survive
Seven seams cover everything from a baby blanket to a bag, and they are not interchangeable. Four of them sit flat, one adds a deliberate ridge, one is a lattice, and one is no seam at all.
| Seam | What it gives you | Reach for it when |
|---|---|---|
| Whip stitch, back loops | Flat, small bars on the surface, fast | A scrappy blanket, joining yarn close to the final round |
| Mattress stitch | The flattest and least visible of the needle seams | Heirloom work, gifts, a single colour blanket |
| Slip stitch, back loops | A tight low cord along the join, very strong | Cushions, bags, anything that gets sat on |
| Single crochet, back loops | A raised stitch ridge you can see | A deliberate contrast frame around every square |
| Flat braid, also sold as simulated braid | An open ladder or lattice between squares | Airy blankets, scrap yarn, decorative joins |
| Join as you go | No seam, worked into the last round | A layout you have already planned |
| Zigzag or chain join | A wavy, lacy gap between squares | Light shawls and summer blankets |
Yarn choice matters more on the seam than in the square. Use the same weight as the squares, because a thinner joining yarn makes a weak seam that pulls out in the wash and a thicker one leaves a cord that will not drape. Buy the joining colour first and in one dye lot, and buy more of it than you think the seams need, since a join of any kind uses about a tenth of the blanket’s total yarn and a braid join uses noticeably more. There is one more measure that decides speed. A 5 in edge on a worsted square holds about 20 double crochet stitches at four stitches to the inch, and every needle seam here puts one pass through each of those, so a single edge is roughly 20 movements and a 10 by 12 throw is 240 edges. That is the real reason people give up on joining: it is not difficult, it is long, and it is far longer if you pick a four-pass needle seam for a blanket that a two-pass whip stitch would have carried.
A blanket is 20 percent crochet and 80 percent joining. Pick the seam you will still be willing to work at square 90, not the one that looks best on the first two.
Step 3: Whip Stitch, One Pass Per Stitch
Thread a tapestry needle with a length of yarn about three times the edge you are joining, and no longer, because long lengths fray and twist. Leave a 4 in tail. Do not knot it. Lay the two squares side by side, both right side up, edges touching, and work the first few stitches over the tail to lock it down. Then it is a wrapping motion and nothing more:
- Bring the needle up through the back loop only of the first stitch on the left square.
- Cross over the join and go down through the back loop only of the matching stitch on the right square.
- Come back up through the next back loop on the left square, and carry on to the end of the edge.
Two decisions do all the work. Working through the back loops only puts the seam behind the fabric, where it flattens instead of standing up, and keeping to one pass per stitch gives you even spacing of about 1/4 in that matches the stitch rate underneath, so the seam can stretch with the squares rather than fighting them. Then resist the pull. Tugging each stitch tight gathers the edge in and leaves a ripple no amount of blocking removes. Work the whole edge relaxed and snug the run at the end instead, a few inches at a time, until the seam lies flat against the table.
Step 4: Mattress Stitch, the Seam You Cannot See
The mattress stitch, called ladder stitch in dressmaking, is the one that survives a photograph. It is worked from the right side, with the squares lying open beside each other rather than stacked.
Find the horizontal bar that sits between the tops of two stitches. That bar is your ladder rail. Take the needle under the bar on the left square, then under the matching bar on the right square, and keep zigzagging back and forth up the edge. Do not pull as you go. Sew three to five passes, then draw the working yarn up and watch the two squares zip together into a flat seam with no visible thread.
Two details decide whether it stays invisible. Work through the back loop of each stitch so the front loop keeps its shape, and keep the passes loose until the run is complete. A mattress stitch pulled tight at every pass puckers the squares permanently, because the pulled yarn has nowhere to give.
The four square junction is where hand-sewn blankets either look professional or look home made. When four corners meet, take the corner chain of all four squares in one pass rather than four separate knots, and carry the zigzag straight through the junction in the same rhythm. The video below shows the motion at full speed, which is easier to copy than a diagram.
Step 5: Slip Stitch and Single Crochet, Worked With a Hook One Size Down
Crocheted joins are faster than needle seams and much less forgiving. Use a hook one size smaller than the one you crocheted the squares with, so a 5 mm square is joined with a 4.5 mm hook. Joining with the same hook leaves a seam looser than the fabric around it, and a loose seam on a crocheted blanket reads as a mistake.
For the slip stitch join, hold the squares right sides together, insert the hook through the back loop of the first stitch on the front square and the back loop of the matching stitch on the back square, then pull a loop through both and through the loop on the hook. Chain one to start and slip stitch across the edge, one slip stitch per pair of stitches. For the single crochet join, do exactly the same but work a single crochet into each pair, which gives the raised ridge that reads as a decorative frame rather than a seam.
Tension is the whole game here. The join should drape like the squares. If the blanket starts to cup or the seam line draws in, you are holding the yarn too tight, and loosening the grip is a real fix, not a hopeful one. The second video works the invisible slip stitch version, which hides the join behind the fabric using the same mechanics.
Step 6: Join the Squares Into Rows, Then Join the Rows
Order is free to get right and expensive to get wrong. Lay every square out in the finished arrangement, move them until the colours balance, then photograph the layout and pin a number to each row. That photograph is what saves you when you are 60 squares in and cannot remember whether the mustard went fourth or fifth from the left.
Then work in one direction only. Join all the squares in row one into a strip, then row two, and so on to the end. Only when every strip is complete do you join strip to strip, working across rather than along. Two reasons: a strip is easier to hold flat than a whole blanket, and working all the horizontal seams before any vertical seam keeps the tension consistent instead of alternating directions and getting a quilted, wavy panel.
Keep three checks as you go. Count the stitches in each strip before you join it to the next, because one strip with an extra cluster will not match. Keep the seam on the same side of the work throughout, so the front of the blanket is consistently the front. And when you reach a junction where four squares meet, deal with it deliberately: one pass through the corner chains of all four, or the same zigzag rhythm carried straight through, never a knot.
Step 7: Join as You Go, and the Braid Seam When You Want a Feature
Join as you go is not a seam at all, which is exactly why it is worth knowing. You crochet the final round of each new square straight onto the squares already finished, so there is nothing left to sew at the end.
The mechanics are small. On a side where the new square meets a finished one, replace each chain space of the final round with a slip stitch worked into the corresponding space or stitch of the neighbour. At a corner, work chain one, slip stitch into the neighbouring corner space, chain one, and carry on with the corner cluster. The square is attached before you fasten off, and a full blanket needs no finishing session at all.
The braid join is the other end of the scale: a deliberate ladder or lattice worked between the squares, made by chaining loops and anchoring them alternately on the two edges. It uses noticeably more yarn than a flat seam, so buy an extra skein of the joining colour, and it leaves visible gaps, which suits an airy blanket and is wrong for anything that needs to be warm or washed hard.
If the pieces being joined are curved rather than square, the same seams work but the stitch counts will not match at the edge, and how to sew together crochet pieces covers that case. This is also where the joining colour earns its keep. One contrasting join, black, cream or a single grey, frames every square and pulls a scrappy mix of colours into something that looks planned. A join in the same colour as the final round disappears, which is the right choice when the squares are already the design.
Block the Squares First, and the Blanket After
Blocking is two separate jobs on this project and both matter. The first is before joining, to bring every square to one measurement. The second is after the border, to settle the whole blanket into a rectangle.
How you block depends on the fibre. Acrylic responds to heat rather than water: pin the square to size, hold a steam iron an inch above the fabric, let the steam settle in, and leave it flat until it is completely cool, because acrylic takes its shape as it cools. Never press the iron onto the stitches, which flattens them permanently. Wool blocks wet: soak in cool water for 20 minutes, roll in a towel to remove the water, pin out to measurement and leave for a day. Cotton is happiest misted and pinned, and it will drop slightly when it dries, so pin a fraction over the target.
Block the squares to one measurement, not to a shape. A square pulled 1/4 in out of true while soft will still be 1/4 in wrong once it dries, and every seam around it will carry that error.
Then finish the outer edge, because a joined blanket has one raw seam line all the way round. A round of single crochet, or double crochet for a deeper border, covers the seam ends and squares the corners. Work it at the same tension as the squares, not tighter.
The Five Faults You Will Meet
Nearly every complaint about joining is one of five faults, and each has a single likely cause.
| What you see | What is causing it | The fix |
|---|---|---|
| The seam ripples and waves | More seam stitches than edge stitches | One pass per stitch, no doubling up |
| The seam puckers and cups | Each stitch pulled tight as it was worked | Sew the run, then snug it in short lengths |
| A lump where four squares meet | Too many stitches crowded into the corner chain | One pass per corner, or all four at once |
| Thread shows on the front | Front loops instead of back loops | Back loops only, front side out |
| Squares drift out of line | Unblocked squares of different sizes | Block and measure before you join |
Work through them in that order, because the first two account for most of the trouble and both are cured by changing how hard you pull rather than by unpicking anything. The fifth one is worth a word of warning: if the squares were never blocked and the drift is more than a quarter inch, no seam will save the blanket. Block a stack before you sew, not after.
Frequently Asked Questions
Which method makes the flattest join on granny squares?
The mattress stitch, also called ladder stitch or invisible seam, worked through the back loops from the right side. It puts the thread inside the fabric instead of on the surface, so the seam disappears. A whip stitch through the back loops is second and much faster, and a slip stitch with a hook one size down is the flattest crocheted option.
Should the squares be right sides together or right sides out?
It depends on the join. For a whip stitch and a mattress stitch, lay the squares right sides out, edges meeting, so the seam sits behind the work. For a slip stitch or single crochet join worked through the back loops, hold the squares right sides together if you want the seam hidden, or right sides out if you want the ridge to show on the front.
Do I have to use the same yarn to join as I crocheted with?
Same weight, ideally the same yarn. A thinner joining yarn makes a weaker seam that can pull out under washing, and a thicker one leaves a stiff cord that will not drape with the blanket. If you want a different colour for a frame, use the same weight in a contrast shade rather than a heavier yarn.
How long should the tails be, and should I knot them?
Leave a 4 in tail at each end of a seam and work the first few stitches over it to anchor it. Weave the remaining 2 in back through the seam in two directions and trim. Do not knot: knots work loose in the wash and leave hard points that show through the seam.
Should I block before or after joining?
Both. Block the individual squares first so they all measure the same, otherwise the seams have to absorb the differences and the blanket will not lie flat. Then block the finished blanket, border included, to settle it into a rectangle and even out the seams.
How many squares do I need for a throw blanket?
At 5 in squares, a 48 x 60 in throw needs 120 squares in a 10 by 12 grid. At 6 in squares the same throw needs 80 in an 8 by 10 grid. Measure your own blocked square first, because a half inch difference changes the count by dozens.
Conclusion
Joining is the part of a granny square blanket that decides whether the finished thing looks made. Measure and block first, pick the seam that matches the job rather than the photograph, work in strips and then join the strips, and pull the runs rather than the stitches. Do those four things and the seams disappear into the blanket, which is exactly what they are supposed to do.
None of it needs special tools: a tapestry needle, a hook one size smaller than the one you crocheted with, and a ruler will carry the whole project. The rest is patience applied in the right order.
What is the seam you keep coming back to on your own blankets, and is it the one that looks best or the one you can actually finish?
About This Guide
This guide was written and tested by Mithu, who crocheted and joined the sample squares for each of the seven seams on this page, measured the finished edges, and reworked the whip stitch and mattress stitch tension notes after the first samples rippled. Every figure here comes from a measured square or from the reference patterns cited, not from a product listing.
All images in this article were created using AI.