How Do I Know What Size Watch Strap I Need?

By JackCoHenry Singapore | Bespoke Watch Straps and Fine Leather Goods

Watch strap sizing has two components: lug width (which strap fits your watch) and strap length (which strap fits your wrist). Getting lug width wrong means the strap won't fit the watch at all. Getting length wrong means the buckle sits in the wrong position. Here's how to find both correctly. From JackCoHenry, a bespoke leather atelier based in Singapore.

Part 1: Lug Width — Does the Strap Fit Your Watch?

Lug width is the internal gap between the two lugs on your watch case — the distance the spring bar has to span. It's always measured in whole millimetres. The most common sizes are 18mm, 20mm, 22mm, and 24mm.

Method A: Look It Up (2 Minutes)

Search "[your watch model] lug width" — this works for almost any watch made in the last 60 years. The official spec sheet or watch databases (Chrono24, WatchBase) will give you the answer. This is the fastest and most reliable method for current production watches.

Method B: Measure Directly (Most Accurate for Vintage)

Use a digital caliper — place the jaws inside the lug gap and read the distance. The result should be a whole number; if you get 19.8mm, round to 20mm. A standard ruler can also work in a pinch, though less precisely.

Method C: Measure Your Existing Strap

If the current strap fits correctly, measure its lug end (the wider end that attaches to the watch). That measurement is your lug width.

Lug width must match exactly. A 19mm strap will not fit a 20mm watch. A 21mm strap will not fit between 20mm lugs. There is no acceptable rounding — buy the exact size.

Part 2: Strap Length — Does the Strap Fit Your Wrist?

Strap length is measured in two sections: the long piece (which goes over the wrist and through the buckle) and the short piece (which holds the buckle). Standard sizing is:

Measure your wrist at the point where you wear your watch using a soft tape measure or a strip of paper, then use the table above. If you're between sizes, choose the longer option — a strap that's slightly long can always use the furthest buckle hole; a strap that's too short has no adjustment room.

Part 3: Taper — What Does "20/18mm" Mean?

Most watch straps taper from a wider lug end to a narrower buckle end. A "20/18mm" strap is 20mm at the watch end and 18mm at the buckle. This is standard for most 20mm watches. The taper creates a more elegant profile than a straight-cut strap.

Common taper combinations:

• 18mm straps: 18/16mm or 18/14mm

• 20mm straps: 20/18mm or 20/16mm

• 22mm straps: 22/20mm or 22/18mm

• 24mm straps: 24/22mm or 24/24mm (straight-cut, for Panerai style)

If you're unsure, 20/18mm is the most versatile choice for a 20mm watch. JackCoHenry can make any taper combination — specify when ordering.

Frequently Asked Questions

Q. My lug width is 19mm or 21mm — will I struggle to find straps?

Yes, at standard retail. 19mm and 21mm are uncommon sizes that most production brands don't offer. Bespoke makers like JackCoHenry make these as standard — no custom surcharge. It's one of the reasons bespoke is worth considering even at these sizes.

Q. Does the strap width affect how the watch looks on my wrist?

The lug width is set by the watch — you can't choose a different width. But the taper affects proportion. A stronger taper (more difference between lug end and buckle end) makes the watch look more elegant and elongates the silhouette. A minimal taper reads as sportier and more contemporary.

Q. I'm not sure which hole to use — is there a rule?

The buckle should sit roughly in the middle of the long piece when worn. If you're always using the first or last hole, the strap length isn't right. At JackCoHenry, if you tell us your wrist size, we'll position the holes so the middle hole is the one you'll use most.

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