Zipper Length Calculator

Zipper Length Calculator: Buy the Right Size the First Time

Zippers are sold in fixed lengths, and a zipper cut exactly to the opening length leaves no clearance for the pull tab and stops. This calculator adds a standard installation allowance so you know exactly what length to buy.

The Formula

Zipper Length to Buy = Finished Opening Length + Allowance

Worked Example

A 7" finished zipper opening, with the standard 1" allowance.

Zipper Length = 7 + 1 = 8 inches

How to Use This Calculator

1. Enter the finished opening length in inches.
2. Optionally adjust the allowance (1" is a common default for pull tab and stop clearance).
3. Click Calculate to get the zipper length to purchase, then round up to the nearest commonly stocked size.

Related Calculations

Use with the Seam Allowance Calculator when planning the seam that will hold the zipper.