Watch Band Size Chart (mm)

When a traditional watch takes a "20mm band", that number is the lug width: the distance between the inside faces of the two lugs, the horns that stick out from the case top and bottom and hold the strap via a spring bar. It is the single number that decides which replacement strap or band fits your watch, and it is measured in millimeters. This page is the chart for traditional watches. If you wear an Apple Watch, band sizing works completely differently (adjustable box sizes and numbered stretch-loop sizes instead of lug widths); that is covered in our Apple Watch band size guide. Samsung's Galaxy Watches are the opposite: they do use ordinary millimeter lugs, nearly all of them 20mm, and the model-by-model list is in our Galaxy Watch band size chart.

Standard band widths: the mm chart

Most watches use even-numbered lug widths in 2mm steps (16, 18, 20, 22, 24mm). Odd widths (19mm, 21mm) show up mostly in luxury and vintage watches and are the classic trap: a 21mm watch is common enough that strap makers stock the size, but selection is much thinner than 20mm or 22mm. The chart below maps each width to the case diameters it typically appears on:

Use this as orientation only. Width tracks case style, not just diameter: a slim 40mm dress watch can take 20mm while a chunky 42mm diver takes 22mm. When the chart and your watch disagree, your watch wins.

Lug width meaning: the 30-second version

• What lugs are. The four horns extending from the case at 12 and 6 o'clock. The strap end slides between each pair and is held by a spring bar, a spring-loaded pin that sits in small holes drilled in the lugs.
• What to measure. The clear gap between the inner faces of one pair of lugs, where the spring bar passes. Not the case diameter, not the strap's outer edge.
• How to measure it. Lay a ruler across the lug gap in millimeters and read the inside-to-inside distance, or use calipers for odd widths where 19 vs 20mm matters. Looking straight down at the watch, with the ruler resting on the spring bar, is the least error-prone angle.
• Taper is a separate number. Many straps narrow toward the buckle: a 20mm strap that tapers to 16mm at the buckle is sold as "20/16". The lug end must match your lug width exactly; the buckle end is a style choice, and the buckle itself must match the tapered width, not the lug width.
• Thickness. Roughly 2-3mm reads dressy, 3.5-4mm everyday, 5mm+ bold and sporty. Only a concern on watches with very tight clearance between the lugs, where a padded strap may not seat cleanly.

Lug width by watch model

Every row below is confirmed by at least two independent sources (strap makers' model-specific fitment pages and watch spec databases). The generation matters more than the model name: Rolex's 2020 update moved the Submariner from 40mm/20mm to 41mm/21mm, and mixing those two up is the most common wrong-width purchase in watchmaking.

Two footnotes worth knowing. The Tudor Pelagos FXD uses fixed bars instead of spring bars, so ordinary two-piece straps do not fit it without an open-ended or pass-through design. And within the MoonSwatch range the strap size is the same 20mm for every mission; the collections are a color menu, not a compatibility list. This table expands over time; the companion lug width chart by brand now carries the expanded per-model table with Seiko, Citizen, Fossil, Casio, Tissot, Hamilton, and Orient rows. For a watch not listed in either, measure the lug gap as described above, and remember the MoonSwatch's bigger sibling rule: the Speedmaster Professional it copies also takes 20mm, so one strap genuinely serves both.

Width is not length, and neither is case size

Three different numbers get called "watch band size" and they answer three different questions:

• Lug width (this page) decides whether the strap physically attaches to your watch.
• Strap length (written like 115/75mm) decides whether it wraps your wrist with a sensible amount of tail. A 7 inch wrist and an 8 inch wrist take different lengths of the same 20mm strap; see our strap size by wrist size chart, or the NATO strap length guide for one-piece nylon bands. Once the width and length are right but the fit is still off, adjusting the band (links, clasp, or a new leather hole) finishes the job. Measuring an existing band to replace it, or sizing the spring bar pins themselves? That is covered in the spring bar sizes and band measuring guide.
• Case size decides how the watch head looks on your wrist, and it is really a lug-to-lug question; that is what our calculator, the case size by wrist table, and the lug-to-lug explainer are for. You will also find lug-to-lug and thickness numbers for 25 popular watches in the watch database.

Jewelry follows the same pattern with different numbers: a bracelet is sized like strap length (wrist measurement plus an allowance you choose) and a bangle is sized off your hand instead, and the bracelet and bangle measuring guide works through both with charts.

Sources

• Standard width chart and width-by-case mapping: watchband.direct band size guide (16-24mm table with case ranges), tailorsizeguide.com watch size chart (strap width by case diameter), and cnswatchbands.com strap sizing guide, cross-checked against superglobalcalculator.com (2mm-step standard widths).
• 1mm-too-wide / 1mm-too-narrow fit failure and even-vs-odd widths: watchband.direct and epochstraps.com guides, both stated explicitly.
• Taper and buckle width rules: cnswatchbands.com and epochstraps.com. Thickness bands: epochstraps.com.
• Rolex lug widths: honcosstraps.com Rolex lug width table, elestraps.com Submariner strap size page, and everestbands.com Rolex dimensions by reference (three sources, all in agreement).
• Speedmaster Professional 20mm: delugs.com Speedmaster strap pages, bernardwatch.com spec listing (42mm case, 20mm lug width), cnswatchbands.com. Seamaster Diver 300M 20mm: augleather.com Omega strap guide, flyback.ai reference specs, cnswatchbands.com.
• MoonSwatch 20mm (all missions): watchbandit.com MoonSwatch strap guide, delugs.com FAQ, strapsco.com MoonSwatch page.
• Tudor widths: vgreenco.com Tudor strap reference, mgbwatches.com Tudor strap listing, cnswatchbands.com Black Bay guide; Pelagos 39 at 21mm additionally confirmed by Hodinkee's hands-on (which corrected its own initial 20mm figure to 21mm).
• Seiko 5 SNK807/805/809 at 18mm (37mm case): strapsco.com model page, watchbandexpert.com original Seiko strap listing, ewatchparts.com fitment listing.