Hat Cast-On Calculator
A hat has to finish smaller than the head or it rides up. Taking about 10% off the measured circumference is the usual starting point, and a very stretchy rib can take more.
Your numbers
Cast-on stitches
101sts
Finished width
50.4cm
Formula
Cast-on stitches = Head circumference × (1 − Negative ease ÷ 100) × Stitches per 10 cm ÷ 10
Round to a multiple of the pattern repeat. A 2×2 rib needs a multiple of four or the join will not line up.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Head circumference (cm)The head at its widest, taped just above the ears. | 56 | 20 and up |
| Negative ease (%)How much smaller than the head you knit — what keeps a hat on. | 10 | 0 ~ 30 |
| Stitches per 10 cm (sts/10 cm)Stitches in 10 cm. If you measured over 5 cm, double it before entering. | 20 | 1 and up |
Step by step
Quick reference table
Results when only Head circumference (cm) changes and everything else stays put.
| Head circumference (cm) | Cast-on stitches (sts) | Finished width (cm) |
|---|---|---|
| 28 | 50 | 25.2 |
| 42 | 76 | 37.8 |
| 56 | 101 | 50.4 |
| 84 | 151 | 75.6 |
| 112 | 202 | 100.8 |
What each result means
| Result | At default values |
|---|---|
| Cast-on stitches (sts)Stitches to cast on; round to the pattern repeat. | 101 |
| Finished width (cm)The width when finished, before any seam or fold allowance. | 50.4 |
Common mistakes
Round to a multiple of the pattern repeat. A 2×2 rib needs a multiple of four or the join will not line up.
Glossary
- Head circumference
- The head at its widest, taped just above the ears.
- Negative ease
- How much smaller than the head you knit — what keeps a hat on.
- Stitches per 10 cm
- Stitches in 10 cm. If you measured over 5 cm, double it before entering.
- Cast-on stitches
- Stitches to cast on; round to the pattern repeat.
- Finished width
- The width when finished, before any seam or fold allowance.
Frequently asked questions
Q. How is Hat Cast-On Calculator calculated?
Cast-on stitches = Head circumference × (1 − Negative ease ÷ 100) × Stitches per 10 cm ÷ 10 — A hat has to finish smaller than the head or it rides up. Taking about 10% off the measured circumference is the usual starting point, and a very stretchy rib can take more.
Q. Can you walk through an example?
With Head circumference 56cm, Negative ease 10%, Stitches per 10 cm 20sts/10 cm, the answer is Cast-on stitches 101sts.
Q. What do I need to enter?
Enter Head circumference, Negative ease, Stitches per 10 cm. 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 Head circumference (cm) moves the answer to Head circumference (cm) 28 → Cast-on stitches (sts) 50 and Head circumference (cm) 112 → Cast-on stitches (sts) 202. 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?
Round to a multiple of the pattern repeat. A 2×2 rib needs a multiple of four or the join will not line up.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.