Zipper gauge refers to the width of the zipper teeth. It is measured in either millimeters or inches. The wider the teeth width, the stronger the cross-wise chain strength. The larger the zipper gauge, the studier the zipper and the heavier or thicker the fabric it could be sewn onto, regardless of the type it is categorized into.
It is pretty easy to measure the zipper gauge. Place the zipper you would like to measure on a horizontal surface. Zip it up completely and measure the teeth width from left to right with the help of a ruler or a tape. The measurement should correspond to those numbers, like 3, 4, 5, 7, etc. For example, the teeth width of a 3# gauge zipper amounts to approximately 3.1-3.5 millimeters. Learn more about our Standard Zipper Size/Teeth Width Specification Charts.
The wider the zipper width, the larger the number measured. This applies to various types of zippers. Let us take metal teeth zipper for example.
from left to right: 3.5#, 4#, 5#, 8#, 10#
In most cases, you should be able to judge the zipper gauge based on the number imprinted or embossed on the back of the sliders, as these numbers regularly stand for the teeth width.
However, there might not be any numbers marked on the sliders and there are also chances that these numbers refer to something else rather than the accurate zipper gauge, say the moulds from which they are casted. Follow the above-mentioned method for double check in both cases.