How to Measure Watch Strap Size | Fits in Minutes

Watch strap size is measured by the lug width — the inside distance between the lugs — and it determines which straps fit your watch.

Getting the right watch strap size matters more than it seems — no one wants to order a strap that arrives too wide or too narrow. You don’t need special tools, just a ruler that shows millimeters and a watch you can remove the band from.

Here’s the core idea: the key figure is the lug width, which is the distance between the two lugs on the watch case where the strap attaches. You also need the strap length to make sure the band actually fits your wrist. Measuring both correctly up front saves you the hassle of returns and helps when you compare 18mm leather watch strap options you’ll find later.

Which Measurement Actually Matters?

Watch strap size comes down to two separate numbers, and confusing them is the most common mistake people make. Lug width controls compatibility; strap length controls fit.

Retailers treat lug width as the primary compatibility measurement — if the width doesn’t match, the strap won’t attach to the watch at all. Strap length matters only after you’ve got a compatible width.

Here’s how the pieces fit together:

• Lug width: the inside distance between the lugs, in millimeters — almost always a whole number from 16mm to 24mm.
• Strap length: for two-piece straps, expressed as two lengths like 110/70mm — the tail side and the buckle side, measured without the buckle.
• Single-piece straps: sometimes listed as one total length, such as 200mm.

If you’re shopping for a replacement, matching the lug width to the watch case is step one. Length is step two.

Sizing a Watch Strap: The Lug Width Method

Lug width is the single number that decides whether a strap fits your watch, and you measure it between the inside edges of the lugs.

Timex’s own guide explains the process simply: measure the lug width between the inside points of the lugs in millimeters. Kohl’s watch band sizing guide adds a useful tip — fit a millimeter bar between the lug ends to get the true width.

1. Remove the current strap so the lugs are exposed.
2. Place a millimeter ruler or digital calipers between the inside edges of the lugs.
3. Read the distance in millimeters — common sizes run from 16mm to 24mm, almost always as a whole number.

For tapering straps, the buckle end is narrower than the lug width; a strap listed as 20/16mm means 20mm at the lugs and 16mm at the buckle.

Measuring Strap Length and Wrist Size

Once the width matches, the length determines comfort. For a two-piece strap, measure the tail/holes side and the buckle side separately with the buckle excluded.

If your current strap fits well, measure each piece flat end-to-end — that’s a reliable reference. If you’re starting fresh, measure your wrist circumference where you wear the watch. Wrap a flexible tape, paper strip, or piece of string around your wrist, mark where it overlaps, and compare the number to a retailer’s length guide.

Timex advises one extra step: subtract the watch case width from your wrist measurement so the strap isn’t too long. That keeps the band from wrapping awkwardly far past the case.

Published sizing guides offer rough starting points.

Apple’s official size guide takes the same approach for smartwatch bands: wrap the sizing tool where you’d wear the watch, secure it with sticky tape if needed, and read the number where the arrows point. The principle is identical across analog watches and smartwatches — measure the lugs for width, measure your wrist for length.

Common Mistakes That Ruin the Measurement

Most sizing errors come down to five easy-to-make mix-ups. Avoiding them keeps your strap order right the first time.

• Measuring the outside of the lugs instead of the inside gap — this adds a few millimeters and makes the strap too wide.
• Using inches without converting to mm — strap widths are sold in millimeters, so match that unit.
• Measuring the old strap instead of the watch case — straps shrink and age, so the strap’s width may not match the lugs anymore.
• Including the buckle when measuring strap length — the buckle adds a few millimeters and skews the fit.
• Assuming width and length are interchangeable — width is lug spacing, length is wrist fit.

If you’re buying a new leather strap for a 18mm lug width, check our tested roundup of the best 18mm leather watch straps to compare options side by side. Once the lug width matches and the length fits your wrist, you’re done — the hardest part of strap shopping is behind you.