Granny square blanket calculator

Making a blanket from joined squares? This calculator works out how many squares across and down you need for your size, the finished size once the joins and border are added, and the yarn for the squares and for joining them. It also shows the smaller and larger layouts either side, so you can choose.

How to use the calculator

1. Enter the blanket size and the border you will add around the outside.
2. Measure one blocked square and enter its size.
3. Choose the joining method. Leave the join width blank to use the usual width for that join, or measure two joined squares and enter it.
4. Measure or weigh the yarn one square uses, and enter your ball length.
5. Compare the smaller, closest and larger layouts.

How the calculator works

Each square plus one join is the repeat. A row of N squares has only N − 1 joins between them, so one join is added before dividing:

Squares across = (body width + join) ÷ (square + join), rounded

The same works for the length. The body is the blanket size minus the border on each side. The finished size adds up the squares, the joins between them and the border.

If you leave the join width blank, the calculator uses the usual width for your join: 0 for whipstitch or mattress stitch, ⅛ in (3 mm) for a slip stitch join, ¼ in (6 mm) for a single crochet join and ½ in (13 mm) for a flat braid join.

The joining yarn comes from the seams: inside edges = (across − 1) × down + (down − 1) × across, each one square long. That seam length is multiplied by a rule of thumb for each join from the research behind these calculators: about 1.5 times for whipstitch, 2.2 for slip stitch, 3.2 for a single crochet join and 4 for a flat braid.

Reading your results

• Squares across × down and squares to make.
• Finished size: with the joins and border.
• Yarn for the squares, squares per ball and balls including joining.
• Yarn for joining: an estimate; join two squares and measure to refine it.
• Smaller, closest and larger layouts: grid, squares and finished size for each.

Worked example

A 50 × 60 in throw with a 2 in border, 5 in squares using 28 yd each, and a single crochet join (¼ in).

• Body: 46 × 56 in. Across: (46 + 0.25) ÷ 5.25 = 8.81, so 9. Down: (56 + 0.25) ÷ 5.25 = 10.71, so 11.
• 9 × 11 = 99 squares, finishing at 51 × 61.5 in with the border.
• Seams: (9 − 1) × 11 + (11 − 1) × 9 = 178 edges, 890 in in all, so about 79 yd of joining yarn.
• Squares: 99 × 28 = 2,772 yd. A 220 yd ball makes 7 squares; 13 balls in all including joining.

With a flat braid join instead (½ in), the same blanket needs 8 × 10 = 80 squares.

Accuracy and limits

• The layout is exact arithmetic, covered by our automated tests. The joining yarn is an estimate.
• Squares joined as you go with a lacy last round: count that round in the square size and set the join width to 0.
• Border yarn is not included: use the border yarn calculator.

Common mistakes

1. Measuring squares before blocking. Granny squares often grow a little when blocked; measure blocked squares, as they will be in the blanket.
2. Ignoring the joins. A ½ in join between every square adds several inches to a big blanket.
3. Counting all four edges of every square as seams. The outside edges are not joined; only the inside edges count.

Tips for more accurate results

• Join two squares and measure the yarn you used, to refine the joining estimate.
• Plan the colours with the granny square colour planner.
• Mixing large and small squares? Use the mixed-size layout planner.

Frequently asked questions

Related guides and tools

• Classic granny square pattern