How to Measure a Zipper (Gauge/Size and Length) 

When we talk about measuring a zipper, there are 2 measurements to consider: Zipper Gauge (Size) and Zipper Length. This guide will show you how to measure both.

How to Measure Zipper Gauge / Size

Also known as zipper size, the gauge of a zipper refers to the width of its teeth, in millimeters, when it’s zipped shut. Whenever you see a number and hash symbol (e.g., #2) next to a zipper, this is referring to the zipper’s gauge.

The larger the number, the heavier the gauge. Here are some examples of the most common zipper gauges and their uses:

Measuring zipper gauge is easy. Measure the zipper teeth, in mm, horizontally when the zipper is closed. Make sure you don’t include any tape in your measurement – it’s just the teeth you want to measure.

You can use a measuring tape, ruler, or digital caliper. If your measuring tool only includes cm and inches, convert them to mm to figure out the gauge (1cm = 10 mm; 0.25” = 6.35mm).

If you’re working with a broken zipper that no longer closes, you can work out its gauge by measuring one side and doubling it. You might have to round up or down slightly, but it should be fairly clear what the gauge is based on the measurement of a single side.

Some guides suggest looking at the back of the slider to determine the zipper gauge, but this isn’t always a good idea. There can be various letters and numbers on the back, which can mean different things depending on the manufacturer.

A number with a hash symbol could refer to the zipper’s gauge. However, considering it’d be best to measure the zipper to confirm, you might as well skip the first step and go directly to measuring it! To correctly determine the zipper’s gauge, this is the best option.

How to Measure Zipper Length

Generally, measuring the length of a zipper is easier than measuring gauge.

Zipper length is often measured in inches. The guidelines for measuring a zipper's length differ slightly based on type of zipper. Regardless, you never include any zipper tape where there’s no chain in your measurement. To put it another way, zippers will always have some extra tape at the top and sometimes on the bottom, which is usually for cutting and sewing depending on the project. You don’t include this in your length measurement, as it’s essentially “waste” material in this regard.

Closed-End Zippers

Closed-end zippers are pretty easy to measure because they have obvious ends. Measure the length from the top of the top stop to the bottom of the bottom stop to get the required length.

Separating Zippers (One-Way)

Also known as open-end zippers, these are just as simple to measure. Go from the top of the top stop to the bottom of the retainer box, which is the part that keeps the zipper on its chain.

Two-Way Separating Zippers

Two-way separating zippers don’t have retainer boxes at the bottom, as the second slider covers this purpose. As such, you’ll want to measure from the top of the top stop to the bottom of the reinforcement tape.