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, and, therefore, the heavier the zipper.

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).

Some guides suggest looking at the back of the zipper's slider to determine the zipper gauge, but this isn’t the best solution. The letters and numbers on the back can mean a whole host of things, depending on the manufacturer.

The best - and most reliable - way to determine a zipper's gauge is to measure the zipper yourself.

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 (to account for any overlap that occurs when the teeth are closed), but it should be fairly clear what the gauge is based on the measurement of a single side.