How many granny squares do I need for a blanket?

Squares needed by blanket size

Pick the blanket size and your square size. Each cell gives squares across × squares down, then the total. These counts are for the squares only: if you’re adding a border, take its width off both sides of the blanket first, as in the example further down.

We rounded each direction to the nearest whole square, so the grid can come out a few centimetres over or under the target. Baby and throw sizes are common ones listed by Jera’s Jamboree; bed sizes are UK mattress tops from Which? magazine.

Measure the square at its final round

Many patterns give a tension check partway through the square, and the finished square is bigger. Becky Skuse’s baby blanket squares measure 7.5cm before their joining round and 9cm after it, a fifth bigger. Attic24’s Harmony squares are checked at 10cm after five rounds, then get a sixth round that joins them.

Make two or three squares exactly as you’ll make them for the blanket, including any joining round, block them if you plan to block the blanket, and measure those. That’s the size to divide by.

Joins add surprisingly little

In the patterns we checked, the join itself barely changed the size. Jera’s Jamboree’s Blossom Cottage uses 6 × 6 squares of 7 inches, joined with mattress stitch, and measures 42 × 42 inches before the border: exactly the squares and nothing more. B.Hooked’s join-as-you-go blanket comes out at the squares plus its 1-inch border, in all three sizes.

A crocheted seam does add a few millimetres per join. Across 3 squares of 29cm, The Patchwork Heart’s Paintbox Blanket ends up at about 90cm with its border, so the seams aren’t adding much there either. If you’re planning dozens of squares across, join two and measure the pair to be sure.

The border is where the size comes from

A narrow border of a round or two adds a few centimetres overall. Wider borders add a lot more. Becky Skuse’s four-round border takes her 90cm grid to 100cm. Annie Design Crochet’s floral blanket grows from a 75 × 90cm grid of squares to 86 × 102cm. Jera’s six-round bobble border adds 5 inches, taking 42 to 47.

Attic24’s Harmony is the extreme case. Nine squares of 10cm give 90cm, yet the finished blanket is 115cm wide. Part of that is the sixth round on every square, measured after the tension check, and the rest is an eight-round border. Decide on the border before counting squares, or you’ll end up with a blanket much bigger than you meant.

Worked example: a single-bed blanket in 15cm squares

You want about 120 × 175cm and a border roughly 5cm wide. Take 10cm off each dimension for the border on both sides, leaving 110 × 165cm for the squares.

At 15cm per square, 110 ÷ 15 is about 7.3, so 7 squares across. 165 ÷ 15 is 11 squares down. That’s 7 × 11 = 77 squares, a 105 × 165cm grid, and roughly 115 × 175cm once the border is on. If you’d rather go slightly over than under, use 8 across and plan for 125cm.

How big a square gets per round

As a starting point, a three-round granny in DK on a 4mm hook is about 7cm (Attic24’s solid granny square). Five rounds in DK on 4mm comes to about 10cm, the tension Attic24 and Cherry Heart both give. In aran on a 5mm hook, Bella Coco gets 10cm after four rounds.

After that, each extra round adds roughly 2cm. The Crochet Swirl’s Amethyst blanket in Stylecraft Special DK is about 103cm after 50 rounds plus a border. Your own tension decides the real number, so measure a sample.

Then work out the yarn

Once you know the number of squares, weigh a few finished ones and use the granny-square planner to turn that into metres and balls, with the joining and border yarn kept separate. If you just want a ballpark first, our guide to blanket yarn quantities has ball counts by blanket size, taken from published patterns.

Common questions

Sources and scope

• attic24.co.uk/posts/harmony-blanket/
• simply-yarn.com/crochet-patterns/easy-free-granny-square-baby-blanket-crochet-pattern
• www.anniedesigncrochet.com/floral-granny-square-blanket-free-crochet-pattern/
• www.anniedesigncrochet.com/scrap-buster-cal-free-granny-crochet-blanket-pattern/
• www.jerasjamboree.co.uk/granny-square-blanket-blanket-blossom-cottage/
• www.thepatchworkheart.co.uk/2015/09/the-stylecraft-blog-tour-paintbox.html
• www.stitchandstory.com/blogs/our-journal/chunky-granny-square-blanket
• sarahmaker.com/granny-square-blanket/
• bhookedcrochet.com/2024/10/08/how-to-make-a-classic-granny-square-blanket-in-3-sizes/
• attic24.co.uk/posts/solid-granny-square/
• www.cherryheart.co.uk/2016/03/giant-granny-square.html
• blog.bellacococrochet.com/granny-square-blanket-free-crochet-pattern/
• thecrochetswirl.com/amethyst-granny-square-blanket/
• www.jerasjamboree.co.uk/baby-blankets-to-crochet/
• www.which.co.uk/reviews/mattresses/article/uk-mattress-sizes-bed-mattress-size-guide-aDx4r9b4T99o
• www.jerasjamboree.co.uk/marlowe-crochet-lap-blanket-pattern/

Sources checked 1 October 2026. Label facts come from the linked references; worked purchase examples and arithmetic are our own illustrations.