Underdial
Lug width is the internal gap, measured in millimetres, between the two lugs on one side of your watch case, where the strap attaches. It tells you which replacement straps physically fit your watch. Most men's watches use 18 mm, 20 mm, or 22 mm. Get it wrong by even 1 mm and the strap either won't seat or leaves an obvious gap.
Before you spend money on a replacement strap, leather, rubber, NATO, or steel bracelet, there is one number you absolutely need. Miss it by a single millimetre and the strap either won’t seat in the case or sits there looking crooked. That number is lug width, and it takes about sixty seconds to find.
Lug width is the distance between the two lugs (sometimes called horns) on your watch case where the strap or bracelet attaches. These lugs secure your strap using spring bars, creating the connection between the case and the strap that holds the watch to your wrist. The measurement is always taken inside edge to inside edge on the same side of the case, not from the outside of one lug to the outside of the other, which is a common first mistake.
The most common lug width is 20 mm, but they can range from 16 mm to 24 mm. Straps only come in whole-number widths, usually between 16 mm and 24 mm, so if you measure a half-millimetre, you have probably got an error in your calculation.
Think of it the way you think about shoe width, not shoe length. The case diameter (40 mm, 38 mm, etc.) is the length. Lug width is the width of the slot. The two numbers are largely independent, a 40 mm case watch can have a 20 mm or 22 mm lug width. The two numbers are not related.
A question we hear often: people buy a strap, it arrives, it doesn’t fit, and only then do they go looking for a ruler.
There are three methods, ranked from most reliable to quickest.
Method 1, Digital caliper (most accurate). A digital caliper gives you a reading accurate to 0.1 mm. A millimetre ruler works in a pinch, but the margin for error is higher. On small sizes that margin matters, a 19 mm lug measured as 20 mm means a wasted purchase. Place the caliper tips against the inside faces of the lugs and read the number. Take a second measurement to confirm.
Method 2, Millimetre ruler. Rest a ruler or calipers across the lugs, you don’t even need to take the strap off. Line up with the inner edge of each lug; lug widths are almost always whole numbers.
Method 3, Read the existing strap. Most leather, rubber, and nylon straps have the size stamped or printed on the underside, near the buckle end. You’ll see something like “20” or “20/16” or “20 mm.” That first number is your lug width. The second number, when present, is the buckle width, the strap tapers from 20 mm at the lugs to 16 mm at the buckle.
This method is fine if you are confident the strap that came on the watch was the correct size. It doesn’t help for replacement straps bought elsewhere, or for vintage watches that came on the wrong strap. When in doubt, measure the watch directly.
Pro move: photograph the caliper reading next to the watch so you have it on file for every future strap search.
This one comes up a lot, and the confusion is completely understandable because the names sound nearly identical. They measure entirely different things.
Lug width is the horizontal gap between the two lugs on one side, the slot where the strap attaches. Typically 18, 20, 22, or 24 mm. This is the number for buying replacement straps.
Lug-to-lug refers to the total vertical length of a watch, from the tip of the top lug to the tip of the bottom one, it is how far the watch stretches across your wrist, not around it. A watch may be 40 mm wide, but if the lug-to-lug is 50 mm, it is going to wear big.
The practical split: lug width = which strap fits the watch. Lug-to-lug = whether the watch fits your wrist.
For wrists under 6.5 inches, staying below 47 mm lug-to-lug is a reliable starting rule to avoid lug overhang. Two watches can share the same 20 mm lug width but wear completely differently because one has a 43 mm lug-to-lug and the other has 50 mm. As one reviewer noted comparing an Orient and a Zodiac, the shorter lug-to-lug distance allows the watch to sit more comfortably on the wrist, and visually it looks like a better fit because it takes up less vertical real estate.
If you want to dig deeper into overall wrist proportion and case sizing, our watch size guide covers case diameter and lug-to-lug fit in detail.
| Watch | Case Size | Lug Width |
|---|---|---|
| Seiko 5 Sports SRPD (most refs) | 40 mm | 20 mm |
| Seiko Prospex Alpinist SPB | 38.5 mm | 20 mm |
| Tissot PRX / Le Locle / Seastar 1000 | 39-40 mm | 19 mm |
| Tissot PR 100 / Visodate | 38-40 mm | 20 mm |
| Tissot Seastar 2000 / Couturier | 44-45 mm | 22 mm |
| Orient Bambino | 40.5 mm | 21 mm |
| Hamilton Khaki Field Auto | 38-42 mm | 20 mm |
| Citizen Promaster Diver BN0150 | 44 mm | 22 mm |
| Tudor Black Bay 58 | 39 mm | 20 mm |
| Tudor Black Bay 41 | 41 mm | 22 mm |
The most common lug widths across the Tissot range are 19 mm, 20 mm, and 22 mm. The exceptions are integrated bracelet designs such as the PRX, which require brand-specific adapters or end links. Always verify against your specific reference number before buying, even a model refresh can change the spec.
Most modern watches are designed around even numbers, 18, 20, 22, 24, but plenty of watches break that rule, and the new Rolex Submariner 41 mm is the most famous example, with a 21 mm lug width. For buyers in the sub-$1,000 bracket, Orient and some Tissot dress references are the most common sources of odd-width surprises.
Readers frequently ask about the two-number format they see on almost every strap listing.
A tapered strap is wider at the lugs and narrower at the ends, often by a difference of 2-4 mm. For example, a strap that measures 22/20 mm has a lug width of 22 mm and a buckle end width of 20 mm, it tapers by 2 mm. The first number is the only one you need to match to your watch. The second is the buckle width.
When purchasing a new strap, you will often see measurements like this: the first number indicates the lug width, while the second number represents the buckle end width. Always match the first number to your watch’s lug width.
Tapered straps generally look more refined on the wrist because the narrowing mimics the natural taper of the wrist. Straight (non-tapered) straps are more common on NATO and Perlon styles, where the uniform width is part of the design.
The consequences go beyond looks. Too narrow a strap creates visible gaps and wobble. Too wide and you risk damaging spring bars or the case, and the strap may not seat properly. For metal bracelets, oyster-style links, jubilee-style links, a size mismatch means the bracelet simply will not physically fit between the lugs. Unlike a soft leather strap that might compress 0.5 mm, solid-link bracelets have no give.
Experienced collectors sometimes fit a 20 mm strap on a 19 mm lug width watch, or an 18 mm strap on a 17 mm. On a soft strap you often cannot tell. But the general rule is still: measure precisely, buy the correct size, and save yourself a return.
One situation that trips up even experienced buyers is the integrated case. An integrated lug design means the strap or bracelet flows directly from the case as part of a unified design. The Bell & Ross BR05 is the clearest example: the watch has an actual lug width of just 12 mm, but uses a 24 mm strap because the case architecture is designed around that strap width. Fitting a standard 24 mm strap to this watch is impossible, it requires a strap made specifically for the BR05. Under $1,000, the Tissot PRX is the most common integrated-lug watch buyers encounter. Check before you order anything aftermarket.
Absolutely, and this is the part most buying guides skip.
Lug width is more than a technical spec, it affects the overall look of the watch. A strap that is proportionally too narrow for its case makes the dial look large and top-heavy. A bracelet that is too wide for a slim dress case looks clunky and thick. Some Grand Seiko 44GS cases are about 40 mm in diameter with only 19 mm strap width, and the large polished lugs make the strap look tiny. A bracelet doesn’t look perfect, but it works better than contrasting leather or fabric does. Twenty millimetres would be ideal with the 40 mm case; 19 mm is perfect with a 38 mm version.
When building a multi-watch collection, standardising on a dominant lug width, say, 20 mm, means your strap investments stretch further. A single quality 20 mm leather strap can rotate across a Seiko 5, a Hamilton Khaki, and a Tissot PR 100 without buying three separate straps. Lug width is the one measurement that connects every watch in your collection to every strap on the market. If you use Underdial to audit your watch box, the app surfaces these compatibility overlaps automatically when you check a new watch against your existing pieces, useful for spotting whether a new buy shares strap hardware with something you already own.
This one comes up a lot among buyers who’ve just discovered their Orient Bambino uses 21 mm or their Tissot Le Locle uses 19 mm.
There are not as many options for aftermarket straps in odd lug widths as there are for even ones. But just because a watch has an odd lug width does not mean you are doomed, there are many more great straps in odd widths than you might think. Major retailers like DeLugs, Crown & Buckle, and WatchGecko stock 19 mm and 21 mm explicitly. The selection is smaller, but workable.
Those odd widths catch a lot of flack. It is a major point of discontent to see brands using 19 mm or 21 mm lug spacing, not just because it forces more strap purchases, but because it also feels like those brands are nudging buyers toward brand-original OEM straps. That said, the practical workaround of going one size up in soft materials remains an option many collectors quietly use every day.
| Lug Width | Typical Case Size | Common Examples |
|---|---|---|
| 16 mm | 34-36 mm | Vintage dress, ladies’ pieces |
| 18 mm | 36-38 mm | Tissot T-Race, vintage sports |
| 19 mm | 38-40 mm | Tissot Le Locle, Seamaster Aqua Terra (some refs) |
| 20 mm | 38-42 mm | Seiko 5 Sports, Hamilton Khaki, Tissot PR 100 |
| 21 mm | 40-41 mm | Orient Bambino, Rolex Datejust 41 |
| 22 mm | 41-44 mm | Tudor Black Bay 41, Citizen Promaster |
| 24 mm | 44 mm+ | Panerai Luminor (most refs) |
The pattern is clear: 20 mm and 22 mm cover the overwhelming majority of modern men’s watches. If your model isn’t listed, those are the two sizes to check first.
For strap style decisions, leather vs. rubber vs. NATO vs. steel, our watch strap types guide picks up where lug width leaves off. Once you know the number that physically fits, every other choice is personal.
What is lug width on a watch?
Lug width is the internal distance between the two lugs (also called horns) on one side of the watch case, the slot where the strap end sits. It is always measured in millimetres. Your replacement strap must match this number exactly.
How do I measure my watch's lug width?
Remove or leave on the strap, then rest a millimetre ruler or digital caliper between the inner edges of the lugs. Measure from inside face to inside face, not the outer width of the lugs themselves. Most results land on a whole number: 18, 19, 20, 21, or 22 mm. A second reading confirms accuracy.
What is the difference between lug width and lug-to-lug?
Lug width (typically 18-22 mm) is the horizontal gap where the strap clips in, it tells you which strap size to buy. Lug-to-lug (typically 42-52 mm) is the total vertical length from the tip of the top lug to the tip of the bottom lug, it tells you how much wrist real estate the watch occupies and whether it will overhang a smaller wrist.
What happens if I use the wrong lug width?
A strap that is too narrow leaves visible gaps on both sides and can rattle or twist. A strap that is too wide simply will not seat between the lugs, or may stress the spring bars and damage the case. Even 1 mm off can be a functional problem on stiffer strap materials.
What lug width do popular affordable watches use?
Most Seiko 5 Sports models use 20 mm. The Tissot PRX, Le Locle, and Seastar 1000 use 19 mm, while the Tissot PR 100 uses 20 mm. Orient Bambino uses 21 mm, and the Tudor Black Bay 41 uses 22 mm. Always confirm against the specific reference, even minor model updates can change the spec.
Can I fit a 20 mm strap on a watch with 19 mm lugs?
Experienced collectors sometimes do this, the 1 mm overhang on each side is nearly invisible on soft leather or nylon straps. However, stiffer materials like thick rubber or solid-end-link bracelets won't compress cleanly. For metal bracelets, match the width exactly.
Why do some watches use odd lug widths like 19 mm or 21 mm?
Odd widths are a design or legacy choice by the manufacturer. The current Rolex Submariner 41 mm uses 21 mm, and many Tissot dress models use 19 mm. The practical downside is a smaller aftermarket strap selection compared to the dominant 20 mm standard.