Elastic Length Calculator
Elastic is cut shorter than the body it has to fit. Take 10% off a 76 cm waist for 68.4 cm, add 2.5 cm to overlap the ends, and cut 70.9 cm. The finished loop then has to stretch 11.1% (10 ÷ 90) to reach 76 cm, and that is the demand you are really putting on the elastic.
Your numbers
Elastic length
70.9cm
Formula
Elastic length = Finished length × (1 − Stretch ÷ 100) + Seam allowance
Past about 30% stretch it still goes on but leaves marks all day. Recovery varies a lot between elastics, so wrapping it round the body and finding the comfortable length beats any formula.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Finished length (cm)The length when finished. | 76 | 5 and up |
| Stretch (%)How much you rely on the elastic stretching. | 10 | 0 ~ 40 |
| Seam allowance (cm)Allowance on one edge; it is added on both, so twice over. | 2.5 | 0 ~ 10 |
Step by step
Quick reference table
Results when only Finished length (cm) changes and everything else stays put.
| Finished length (cm) | Elastic length (cm) |
|---|---|
| 38 | 36.7 |
| 57 | 53.8 |
| 76 | 70.9 |
| 114 | 105.1 |
| 152 | 139.3 |
What each result means
| Result | At default values |
|---|---|
| Elastic length (cm)Elastic to cut, relaxed rather than stretched. | 70.9 |
Common mistakes
Past about 30% stretch it still goes on but leaves marks all day. Recovery varies a lot between elastics, so wrapping it round the body and finding the comfortable length beats any formula.
Glossary
- Finished length
- The length when finished.
- Stretch
- How much you rely on the elastic stretching.
- Seam allowance
- Allowance on one edge; it is added on both, so twice over.
- Elastic length
- Elastic to cut, relaxed rather than stretched.
Frequently asked questions
Q. How is Elastic Length Calculator calculated?
Elastic length = Finished length × (1 − Stretch ÷ 100) + Seam allowance — Elastic is cut shorter than the body it has to fit. Take 10% off a 76 cm waist for 68.4 cm, add 2.5 cm to overlap the ends, and cut 70.9 cm. The finished loop then has to stretch 11.1% (10 ÷ 90) to reach 76 cm, and that is the demand you are really putting on the elastic.
Q. Can you walk through an example?
With Finished length 76cm, Stretch 10%, Seam allowance 2.5cm, the answer is Elastic length 70.9cm.
Q. What do I need to enter?
Enter Finished length, Stretch, Seam allowance. 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 Finished length (cm) moves the answer to Finished length (cm) 38 → Elastic length (cm) 36.7 and Finished length (cm) 152 → Elastic length (cm) 139.3. 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?
Past about 30% stretch it still goes on but leaves marks all day. Recovery varies a lot between elastics, so wrapping it round the body and finding the comfortable length beats any formula.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.