Watch strap size gauge for lug width

A free tool for finding the strap size of a watch. Straps are ordered by lug width: the gap between the two lugs, measured between their inner faces, where the strap end and its spring bar sit. It runs in even millimeters for most watches — 18, 20 and 22 are the everyday sizes — with odd 19 and 21 mm on some models. Fit the lugs into a printed slot or read the gap on a calibrated rule to get the width exactly.

Finding your strap size step by step

Remove the old strap

If you can, take the strap off so you are measuring the bare lug gap, not the strap end squeezed inside it.

Measure between the lugs

Read the distance between the flat inner faces of the two lugs — the opening the strap slots into — not the outside of the case.

Or use the slot test

Lower the watch onto the printed slots; the one the lugs sit across without a gap or a squeeze is your lug width.

Note the width for both parts

The tool snaps to the nearest standard width — order the strap and the spring bars in that same millimeter size.

Measure lug width — the one number a strap is sold by

Strap length by wrist

Lug width is one thing, strap length another, and the two get confused constantly. Wrap a tape around the wrist and take the row: the first number is the short buckle half, the second the long punched half.

14–15 cm 70 + 105 mm

15–16 cm 75 + 110 mm

16–17 cm 75 + 115 mm

17–18 cm 80 + 120 mm

18–19 cm 80 + 125 mm

19–21 cm 85 + 135 mm

The series is for a classic buckle strap. A deployant bracelet is not chosen by length but adjusted by links; a NATO comes in one length and the tail tucks back.

What this gauge does

Reads the lug gap, not the case

Measures the inner-face-to-inner-face distance the strap fills, which is unrelated to the case diameter quoted in a watch's marketing.

Labeled slot test

The printed sheet has 16 to 24 mm slots — slide the watch head down until the lugs straddle one cleanly to confirm the width by fit.

Even and odd sizes

Recognizes the common even widths and the awkward 19 and 21 mm sizes that catch buyers out, snapping your reading to the nearest real one.

Matches the spring bar

The same number sizes the spring bars that hold the strap, so one measurement covers both the band and the pins you order with it.

Taper-strap note

Reminds you that tapered straps quote two numbers — lug width and the narrower buckle width — and that the lug end is what must match the watch.

Why the lug gap is the only number that fits

A new strap can be the right material, length and color and still be useless if the lug width is wrong by a single millimeter — too wide and it will not enter the lugs, too narrow and it rattles. Case size, the figure people remember, has nothing to do with it. This tool reads the lug gap by a snug slot fit or a calibrated rule, snaps it to a real even or odd width, and gives you the one number that orders both the strap and its spring bars.

Watch strap sizing questions

Is lug width the same as my watch case size?

No, and confusing the two is the usual mistake. Case size is the diameter of the watch body; lug width is the much smaller gap between the lugs where the strap fits. A 40 mm watch might take a 20 mm strap, so always measure the lug gap, not the case.

Where exactly do I measure the lug width?

Between the inner faces of the two lugs, across the opening the strap drops into. Measure the inside gap, not lug-tip to lug-tip on the outside, because the strap and spring bar only span the inner distance.

Are watch straps only made in even sizes?

Even widths — 18, 20, 22, 24 mm — are by far the most common, but 19, 21 and 23 mm do exist, often on dress watches and some Swiss models. The tool reports the nearest standard width whether it is even or odd, so an odd size is not missed.

Do the spring bars have to match too?

Yes. The spring bars are the sprung pins that lock the strap between the lugs, and they come in the same width as the lug gap. Once you know the lug width you can order the strap and a set of spring bars in one go.

What does a strap mean by "20/16"?

That is a tapered strap: it is 20 mm at the lug end and narrows to 16 mm at the buckle. Only the first number has to match your watch's lug width — the second is just how wide the buckle and keeper are.

My lugs are curved or hidden — how do I measure?

Some sports and integrated-bracelet watches hide the lugs or shape the strap end to the case. Measure the straight opening where a spring bar would sit if you can reach it; if the strap is fully integrated, the watch usually takes only its own model-specific band rather than a standard width.

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Who is this tool for?

💍 Jewelry & Watches

Published 18 May 2026 Updated 08 Sep 2026 Author: The Supreme