How to Measure Your Wrist for a 20mm Watch Band? | Fit Guide

Before you order a replacement strap, you need to settle one thing: 20mm refers to the width of the band, not the size of your wrist. That number describes the gap between the watch case lugs where the band attaches. Your wrist measurement, meanwhile, tells you which strap length will actually wrap around and fasten. Confusing the two is the most common reason a new band arrives and doesn’t fit.

Here is the short version: measure the lug gap with a ruler or caliper, and measure your wrist with a soft tape or string. When the lug gap reads 20mm, you need a 20mm band. Then use your wrist circumference to pick the right length option. The steps below walk through both measurements, along with what to do if your wrist falls outside the standard range.

Measure the Lug Width for Your 20mm Band

The band width must match the lug width of the watch case, and that measurement is independent of your wrist size. A band labeled 20mm fits watches with a 20mm lug gap, and it will not fit watches with different lug widths without adapters.

To get the number:

• Remove the current band so the lugs are fully exposed.
• Place a ruler or caliper across the gap between the inside edges of the two lugs.
• Read the measurement in millimeters. For a 20mm band, that gap should read 20mm.

Measure in millimeters and round to the nearest millimeter when needed. Never force a band into lugs that are narrower or wider than the band width, as an improper fit can affect retention and security. If you have an existing strap that fits well, measuring its width at the lug end is just as reliable as measuring the case itself.

Measure Your Wrist Circumference for Strap Length

Wrist circumference determines which strap length you need, not the band width. Most standard straps fit wrists around 6 to 7.5 inches, so measure yours before ordering to avoid a strap that is too short or too long.

The reliable method:

• Wrap a soft measuring tape around your wrist where the watch normally sits.
• Keep it snug but not tight, so the watch can move slightly on the skin.
• Note the number where the tape overlaps.

If you don’t have a soft tape, use a piece of string, mark where it overlaps, then lay it flat against a ruler. Wrists outside the 6-to-7.5-inch range generally need short or long strap options, which most band makers offer as separate SKUs. Check the product listing for those length variants before purchasing.

Apple Watch owners should note a special case: the Apple Watch uses proprietary attachment hardware rather than standard lug bars, so traditional 20mm straps require an adapter to fit those models.

Apple’s Official Sizing Method

Kohl’s guide takes a slightly different approach: measure the band width between the lug ends, then also measure wrist length and case size to estimate the total band length you need. This combines both measurements into a single estimate rather than treating them separately.

Choosing the Right 20mm Band

Once you have confirmed the 20mm lug width and your wrist circumference, you’re ready to pick a strap. Match the band width to the lug gap exactly, then match your wrist size to the length option, and you have eliminated the two most common fit failures. If you are comparing materials, buckles, and price points across several well-reviewed options, our tested roundup of the best 20mm watch band choices covers the top picks with sizing notes included. For Apple Watch users, filter for straps sold with adapters built in, since standard 20mm bands won’t attach directly.