Measuring a zipper seems straightforward at first, but because you’ll need to get measurements for both the width of the teeth and the length of the zipper, it can sometimes be tricky.
Remembering a few simple tricks can make it much easier to get a correct zipper measurement.
Estimate Based on Use
Zippers are available with different teeth widths. These widths change both the appearance and durability of the zipper, so different tooth widths are used for different applications.
For example, smaller tooth widths are less visible, so they’re often used on clothing, particularly pants, skirts, and fancier jackets. These smaller sizes are also commonly used on cushions and pillows and sometimes small handbags.
Medium zipper sizes are also sometimes used on clothing, but usually only on outer clothing, such as snow jackets or ski pants. They’re also used on larger purses, backpacks, duffle bags, sleeping bags, and tents.
The largest zipper sizes are very durable and easy to grip and use. They are frequently seen on heavy-duty tents, boat or car covers, wetsuits, and some extremely durable outer clothing.
If you’re trying to decide what zipper size you need for a certain application or you want to replace a broken zipper, you can often get a good estimate of tooth size by considering what the zipper will be used for.
Look for a Number
The easiest way to determine the size of a zipper is to turn it over and look for a number. Most zippers have a number printed somewhere on the back.
Often, the number is printed on the zipper pull, but it can also be printed at the top or bottom. Small numbers range from 1 to 4.
Medium zippers range from 5 to 7, and large zippers are numbered between 8 and 10. Some zipper manufacturers also use half sizes.
Measuring in Inches
To get the most accurate zipper measurement, it’s important to get out a ruler or tape measurer and measure both the length of the entire zipper and the width of the teeth.
To determine how long of a zipper you’ll need, first measure the opening where the zipper will go. Then, you’ll need to measure the zipper itself. Zippers are measured from the top end of the slider or pull to the bottom stop, where the zipper ends.
There will be excess fabric or tape at both ends, but this doesn’t count toward the zipper’s length. You’ll also want to allow 5/8 of an inch for seam allowance, and you’ll need to add about 0.5 to 1 inch for eyelets, snaps, or buttons at the top of the zipper.
You can get an exact measurement depending on what secondary closure you’re using. It’s often best to choose a zipper that’s slightly shorter than your opening so you have some leeway for sewing.
Measuring zipper width for size (Gauge)
You can also measure the width of the zipper’s teeth. Size 1 teeth are 0.04 inches across, while size 10 teeth are 0.4 inches or 10 mm wide.
Size 5 or medium teeth are 0.19 inches or 5mm wide.
This video shows how to accurately measure zipper teeth width to determine the size.