Zipper Length Calculator
A 22 cm opening plus 2 cm of allowance top and bottom needs 24 cm — and nobody sells a 24 cm zip. Stock metric sizes step 10 · 12 · 15 · 18 · 20 · 23 · 25 · 30 · 35 · 40 · 45 · 50 · 55 · 60 · 70 · 80 · 90 cm, so you buy the 25. Shops selling in inches step 4 · 5 · 7 · 9 · 12 · 14 · 16 · 18 · 20 · 22 · 24 in.
Your numbers
Zipper size
25cm
Total length
24cm
Formula
Total length = Opening length + Allowance beyond the opening, Zipper size ≥ Total length (10 · 12 · 15 · 18 · 20 · 23 · 25 · 30 · 35 · 40 · 45 · 50 cm)
The stated length measures the toothed run the slider travels, not the tape, which continues past it at both ends. Buying long and shortening only works on coil zips: cut the teeth off a metal or Vislon one and the slider comes off, and a separating zip cannot be touched at the bottom at all.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Opening length (cm)The run that actually has to open, measured on the finished piece. | 22 | 1 and up |
| Allowance beyond the opening (cm)Extra beyond the opening, spent on stitching and finishing the ends. | 2 | 0 ~ 10 |
Step by step
Quick reference table
Results when only Opening length (cm) changes and everything else stays put.
| Opening length (cm) | Zipper size (cm) | Total length (cm) |
|---|---|---|
| 11 | 15 | 13 |
| 16.5 | 20 | 18.5 |
| 22 | 25 | 24 |
| 33 | 35 | 35 |
| 44 | 50 | 46 |
What each result means
| Result | At default values |
|---|---|
| Zipper size (cm)The stated size to buy, rounded up to one that is actually sold. | 25 |
| Total length (cm)The whole length before it is divided. | 24 |
Common mistakes
The stated length measures the toothed run the slider travels, not the tape, which continues past it at both ends. Buying long and shortening only works on coil zips: cut the teeth off a metal or Vislon one and the slider comes off, and a separating zip cannot be touched at the bottom at all.
Glossary
- Opening length
- The run that actually has to open, measured on the finished piece.
- Allowance beyond the opening
- Extra beyond the opening, spent on stitching and finishing the ends.
- Zipper size
- The stated size to buy, rounded up to one that is actually sold.
- Total length
- The whole length before it is divided.
Frequently asked questions
Q. How is Zipper Length Calculator calculated?
Total length = Opening length + Allowance beyond the opening, Zipper size ≥ Total length (10 · 12 · 15 · 18 · 20 · 23 · 25 · 30 · 35 · 40 · 45 · 50 cm) — A 22 cm opening plus 2 cm of allowance top and bottom needs 24 cm — and nobody sells a 24 cm zip. Stock metric sizes step 10 · 12 · 15 · 18 · 20 · 23 · 25 · 30 · 35 · 40 · 45 · 50 · 55 · 60 · 70 · 80 · 90 cm, so you buy the 25. Shops selling in inches step 4 · 5 · 7 · 9 · 12 · 14 · 16 · 18 · 20 · 22 · 24 in.
Q. Can you walk through an example?
With Opening length 22cm, Allowance beyond the opening 2cm, the answer is Zipper size 25cm.
Q. What do I need to enter?
Enter Opening length, Allowance beyond the opening. 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 Opening length (cm) moves the answer to Opening length (cm) 11 → Zipper size (cm) 15 and Opening length (cm) 44 → Zipper size (cm) 50. 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 stated length measures the toothed run the slider travels, not the tape, which continues past it at both ends. Buying long and shortening only works on coil zips: cut the teeth off a metal or Vislon one and the slider comes off, and a separating zip cannot be touched at the bottom at all.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.