What strap length do I need?

Two answers circulate. One says buy Regular, because it fits most wrists. The other says check the maker's chart, because there is no standard. The second is right, but it leaves you reading five charts. We read them: the size tables of Delugs, Artisan Straps, Hirsch, Di-Modell and The Strap Tailor, 19 sizes in all, plus Barton for NATO straps. The labels disagree. The totals, set against the wrist each size is sold for, follow one rule.

The charts side by side

Every figure below is the maker's own, measured without the buckle. Hirsch and Di-Modell figures are as their US retailer Holben's publishes them; the others come from the makers' own size guides. Wrist ranges given in inches are converted at 25.4 mm to the inch and rounded.

The Strap Tailor's chart carries on above 8 inches: 135/80 for 8.1 to 8.5 inches (205 to 215 mm), 140/85 for 8.6 to 9 inches (218 to 228 mm) and 145/90 for 9 inches and over. Those rows complete the 19 sizes behind the rule below.

The rule the charts share: wrist plus about 12 mm

Take the middle of each size's wrist range and subtract it from the strap's total. Across all 19 sizes the difference runs from 0 to 23 mm, and the median is 12 mm. Not one size has a total shorter than the smallest wrist it is sold for; the closest is 6 mm over. Put the other way round: your strap's two pieces should add up to roughly your wrist circumference plus 10 to 15 mm.

That looks backwards, since the watch head covers part of your wrist. The reason is overlap: the long piece passes through the buckle and on through the keeper, and that doubled section is counted in the total. Holben's describes the target as enough tail "to pass securely through the keeper without leaving an excessive amount beyond it"; Artisan's test for too long is a tail you can see on your wrist.

The width of each range comes from the holes. Delugs punches 7 holes 6 mm apart, so from the middle hole you have three holes, 18 mm, of adjustment either way, and its wrist ranges are 25 mm wide. Aim for the middle hole, as our guide to watch sizing and fit explains: it leaves room for a wrist that swells in the heat and for leather that stretches in its first weeks.

Your wrist, size by size

If you have not measured yet, our answer on how to measure your wrist takes two minutes and explains why an afternoon reading is the useful one. Then find your row:

Where a cell offers two sizes, both ranges include your wrist; Holben's advice is to take the shorter for less tail, the longer for more room. Under about 150 mm only Artisan's Extra Small and Delugs' Small reach you on these charts; our answer on the best watch for a small wrist covers the case side of that problem.

Why "Regular" is not one size

Three traps sit in the charts above:

• Regular ranges from 185 to 200 mm. Delugs' Medium is 115/70, Artisan's Standard 115/75, Di-Modell's Regular 115/80 and Hirsch's Regular 120/80. On a 165 mm wrist the 200 mm strap leaves 15 mm more tail than the 185 mm one.
• Hirsch's letters are shifted. Holben's notes that Hirsch prints M for Short, L for Regular and XL for Long. A buyer who reads M as medium gets the short strap.
• Long does not always mean a longer long piece. Hirsch's Long keeps the 120 mm long piece and stretches the buckle piece from 80 to 100 mm. Di-Modell goes from 115/80 to 120/90, Delugs adds 10 mm and 5 mm with each step. The totals still rise, so the rule holds, but where the buckle sits on your wrist changes.

That last point is why Delugs offers split sizes. Its example: a Medium (115/70) whose buckle sits in the middle of the wrist but whose tail shows. The fix is a 105/70, a shorter long piece with the buckle piece unchanged.

Measure a strap you already own

Artisan's second method skips the wrist entirely: measure the long and short pieces of a strap you already own that fits, and add them. Their example is 120 mm plus 80 mm, 200 mm. If that strap feels too long or too short, adjust the total from there. Delugs also prints the distance to the middle hole, 63 mm on its Small, 71 mm on Medium and 81 mm on Large, a figure you can measure on your own strap and compare directly.

Check the width too: our strap and lug width finder converts a lug measurement into the strap and buckle width to order, and our answer on which spring bars you need covers the pins.

NATO and single-pass straps

A NATO strap is one long piece that threads under the watch and back over itself, so it is quoted as a single length, and the length covers a much wider range of wrists than a two-piece strap. Barton sells two: a standard 10 inch (254 mm) strap that "generally fits wrists from 5" to 7 1/2"" (127 to 191 mm) and a long 11 inch (279 mm) strap for 6 to 8 1/2 inches (152 to 216 mm). Barton's own split is simple: wrists under 7 inches typically prefer the standard, over 7 1/4 inches the long. Its Jetson nylon strap comes in one length, 270 mm, for most wrists.

Excess length on a NATO is not a sizing failure. Barton says to fold the free end back into the keeper, or cut it and seal the end with a flame so it does not fray. That forgiveness is one of the trade-offs in our NATO, leather and metal bracelet comparison.

Cut-to-fit rubber and smartwatch bands

Some rubber straps are sold long and cut down. The Strap Tailor ships its cut-to-fit rubber straps to fit the largest wrist "out of the packaging" and tells you to remove one segment at a time, test the fit with the clasp on, and keep more than you think you need. You can cut the two ends unevenly to move the clasp.

Smartwatch bands are sold by wrist range directly. Nike's chart for its Apple Watch Sport Bands gives 140 to 190 mm for the 46 mm S/M band (for 44 to 49 mm cases) and 160 to 210 mm for M/L, and adds that most women's wrists fall within 140 to 175 mm and most men's within 165 to 195 mm. Our smartwatch and mechanical watch comparison covers the rest of that decision.

What moves you up or down a size

The wrist is the main input but not the only one. Delugs says the right length "also depends on the lug-to-lug distance of your watch, and even the shape of your wrist". Two things to adjust for, and then the fit itself, which our answer on how a watch should fit covers:

• A long watch head. The strap starts at the spring bars, so a watch with a long lug-to-lug distance covers more of your wrist and leaves less for the strap to cover.
• A deployant clasp. Holben's says a deployant clasp can change the fit, depending on the clasp, strap and watch, and that a strap made for one should be sized by its own listing, not the general chart.

When this answer stops applying

• The strap is not a two-piece buckle strap. NATO, single-pass, cut-to-fit rubber and smartwatch bands follow the rules in their own sections above, and bracelets are sized by links; see how to shorten a watch bracelet.
• The maker publishes no wrist range. Then the total is all you have: aim for wrist plus 10 to 15 mm, or match a strap you own.
• Your wrist is outside 145 to 210 mm. Of these five makers, only Artisan goes smaller and only The Strap Tailor bigger; most others need a custom length.
• The watch has an integrated or proprietary fitting. The maker's own strap is the only size guide that applies.

If a strap keeps failing, our page on a strap that keeps breaking covers the causes, and our strap and bracelet price guide covers what the replacement should cost. For a wider view of materials and fittings, see our guide to straps and bracelets.

For everything else: add the two pieces, compare the total with your wrist, and expect it to come out about 12 mm longer.