Watch Strap Size Guide & Chart

Strap size is the same thing as lug width

When a strap is sold as “20mm”, that figure is its width at the end that attaches to the watch. It must match your watch's lug width: the inside distance between the two lugs that hold the spring bar. A 20mm lug width needs a 20mm strap. Case diameter, lug-to-lug length and wrist size don't change the number you buy.

If you don't know your lug width, look your watch up in the Strap Index finder, find it in the full chart below, or measure it with our on-screen ruler or printable ruler.

Watch strap size chart by case size

Case diameter doesn't set the strap size, but it narrows it down. The middle column is the usual range; the right-hand column shows what the watches with standard lugs in our index actually use.

The spread inside each band is why you should never guess from case size: two 41mm watches can need 20mm and 22mm straps.

Why a single millimetre matters

Too narrow and the strap leaves a visible gap at each side, slides along the spring bar and wears the strap's edges. Around half a millimetre narrower is usually unnoticeable; a full size down is obvious on leather but often fine on a NATO.

Too wide is worse. The strap either won't go between the lugs at all or has to be squeezed in, which makes it bunch and pushes against the spring bar tips. That's how bars pop out. Never force a wider strap into narrower lugs.

The common sizes, and the watches in our index that use them

Below 18mm you're mostly into women's and small vintage watches. Above 22mm (24mm, 26mm) you'll find oversized pilot and Panerai-style watches.

A useful rule of thumb (and its limits)

Lug width tends to be about half the case diameter. Across the watches with standard lugs in our index, it averages 50% of the case diameter, so a 40mm watch usually takes a 20mm strap. But it's only a guide: the Garmin Forerunner 265S and the Garmin Forerunner 255S both have narrower lugs than their case size suggests. Always look up or measure; never guess from the case size.

Tapered straps: two numbers on the label

Many leather straps narrow towards the buckle. They're listed with two widths, such as 20/18mm or 20/16mm. Only the first number, the lug end, has to match your watch. More taper looks dressier and slimmer; a straight, untapered strap looks sportier and suits dive and tool watches. NATO and perlon straps are the same width all the way along.

Strap length sizes

Width has to match exactly; length just has to suit your wrist. Two-piece straps are listed as long/short pieces:

Makers' sizes vary, so check their chart. Our strap length guide and calculator also checks whether a watch's lug-to-lug suits your wrist.

Odd sizes: 19mm and 21mm

Most watches use even widths, but some use 19mm or 21mm. Straps in those sizes are harder to find, and an even-sized strap is a compromise. We cover your options in 19mm and 21mm watches: finding straps for odd lug widths.

What about smartwatches?

Some smartwatches use ordinary spring bars and standard widths. Samsung Galaxy Watch 6 (44mm), Garmin Forerunner 265 and Huawei Watch GT 4 (46mm), among others, all take normal straps. Others use a proprietary slot or clip that needs model-specific bands or an adapter. See integrated, proprietary and smartwatch straps.

Full watch strap size chart

Every watch in our index, A–Z by brand. Strap size is the lug width; tap a model for spring bars, fit notes and sources.