Granny Square Size Calculator
A motif grows outwards on all four sides, so each round adds twice its own depth to the side. With a round measuring 2 cm, six rounds give a 24 cm square. Asking for 30 cm needs eight rounds (32 cm) because seven stop at 28 — you cannot work half a round, so a target size rarely lands exactly.
Your numbers
Square size
24cm
Rounds needed
8rnds
Formula
Square size = 2 × Growth per round × Rounds, Rounds needed = ⌈Finished width ÷ (2 × Growth per round)⌉
The depth per round comes from the yarn and hook. Round one is a cluster crammed into the centre ring and sits narrower than the rest, and the number of chains at each corner moves every round by 2–3 mm. Work three rounds, measure one side and divide by six — twice the round count, because each round grows both ends of that side. A 12 cm side means 2 cm per round, and that is the number worth putting back into this calculator.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Rounds (rnds)Rounds worked outwards from the centre, as opposed to rows worked back and forth. | 6 | 0 ~ 40 |
| Growth per round (cm)How far one round grows outwards; work three rounds, measure a side and divide by six. | 2 | 0 and up |
| Finished width (cm)The width when finished, before any seam or fold allowance. | 30 | 0 and up |
Step by step
Quick reference table
Results when only Rounds (rnds) changes and everything else stays put.
| Rounds (rnds) | Square size (cm) | Rounds needed (rnds) |
|---|---|---|
| 3 | 12 | 8 |
| 4.5 | 18 | 8 |
| 6 | 24 | 8 |
| 9 | 36 | 8 |
| 12 | 48 | 8 |
What each result means
| Result | At default values |
|---|---|
| Square size (cm)One side of the finished motif, measured after blocking. | 24 |
| Rounds needed (rnds)Rounds needed to reach the target size; there are no half rounds, so it rounds up. | 8 |
Common mistakes
The depth per round comes from the yarn and hook. Round one is a cluster crammed into the centre ring and sits narrower than the rest, and the number of chains at each corner moves every round by 2–3 mm. Work three rounds, measure one side and divide by six — twice the round count, because each round grows both ends of that side. A 12 cm side means 2 cm per round, and that is the number worth putting back into this calculator.
Glossary
- Rounds
- Rounds worked outwards from the centre, as opposed to rows worked back and forth.
- Growth per round
- How far one round grows outwards; work three rounds, measure a side and divide by six.
- Finished width
- The width when finished, before any seam or fold allowance.
- Square size
- One side of the finished motif, measured after blocking.
- Rounds needed
- Rounds needed to reach the target size; there are no half rounds, so it rounds up.
Frequently asked questions
Q. How is Granny Square Size Calculator calculated?
Square size = 2 × Growth per round × Rounds, Rounds needed = ⌈Finished width ÷ (2 × Growth per round)⌉ — A motif grows outwards on all four sides, so each round adds twice its own depth to the side. With a round measuring 2 cm, six rounds give a 24 cm square. Asking for 30 cm needs eight rounds (32 cm) because seven stop at 28 — you cannot work half a round, so a target size rarely lands exactly.
Q. Can you walk through an example?
With Rounds 6rnds, Growth per round 2cm, Finished width 30cm, the answer is Square size 24cm.
Q. What do I need to enter?
Enter Rounds, Growth per round, Finished width. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Rounds (rnds) moves the answer to Rounds (rnds) 3 → Square size (cm) 12 and Rounds (rnds) 12 → Square size (cm) 48. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
The depth per round comes from the yarn and hook. Round one is a cluster crammed into the centre ring and sits narrower than the rest, and the number of chains at each corner moves every round by 2–3 mm. Work three rounds, measure one side and divide by six — twice the round count, because each round grows both ends of that side. A 12 cm side means 2 cm per round, and that is the number worth putting back into this calculator.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.