Watch lugs explained: lug-to-lug, lug width and why they decide fit
What a watch lug is, how to measure lug-to-lug and lug width, why lug-to-lug often decides fit, and which strap fits a 20 mm lug width.
Watch lugs explained: lug-to-lug, lug width and why they decide fit
A watch lug is where the strap attaches, and three numbers describe it: lug width, lug-to-lug and case diameter. Here is what each one means, how to measure it and which tends to decide fit.
A watch lug is one of the pair of projections at the top and bottom of a watch case that the strap attaches to. Three numbers describe how a watch meets its strap and your wrist. Lug width is the gap between a pair of lugs, and it sets the strap width. Lug-to-lug is the length from tip to tip across the case, and it shows how much wrist the watch covers. Case diameter is the width across the case. We are a watch company, so our worked example is the published numbers of the Vannin Field Watch, which is coming soon. For the wrist side, see our guide to how to measure your wrist for a watch.
What is a watch lug?
A watch lug is a projection on each side of the case, usually at the 12 and 6 o'clock ends, that the strap or bracelet attaches to. A spring bar sits between each pair of lugs and holds the strap in place. Some writers call lugs horns, and a few watches put them elsewhere on the case.
The lugs do two jobs. The gap between a pair sets the strap width the watch takes, which is lug width. How far the lug tips reach along the wrist sets lug-to-lug. Both numbers appear on spec sheets and they are easy to mix up, so this page defines each one once and keeps to that wording.
Most lugs are milled with the rest of the case from a single piece. According to Monochrome, that method took hold in the late 1920s and is the most common today, while lugs soldered or welded on separately are now reserved for some high-end work.
Lug-to-lug, lug width and case diameter: the three numbers
Three numbers describe how a watch meets its strap and your wrist: lug width, lug-to-lug and case diameter. The diagram shows all three lug measurements on one outline, drawn to scale with the Vannin Field Watch's published figures.
Two related terms are worth fixing now. Strap width is the width of the strap at the lug end, and it matches lug width. Buckle-end width is a separate figure, taken where the strap meets the buckle.
| Measurement | What it is | What it tells you | Field Watch (published) |
|---|---|---|---|
| Case diameter | The width across the case, which makers usually quote without the crown | The width of the case | 38.0 mm |
| Lug width | The gap between the inner edges of a pair of lugs | The strap width at the lug end | 20.0 mm |
| Lug-to-lug | The tip of the top lugs to the tip of the bottom lugs | The length along the wrist | 46.0 mm |
What is lug to lug on a watch?
Lug-to-lug is the distance from the tip of the top lugs to the tip of the bottom lugs, the full length of the case along the 12 to 6 line. It shows how much wrist the watch covers. It is also written lug to lug, lug-to-lug length or L2L. It is not the gap between a pair of lugs.
The NOMOS glossary defines lug-to-lug as the distance between the outer ends of the lugs and keeps it apart from lug width. NOMOS adds that enthusiasts often point out that makers give diameter and height but hardly ever the outer lug measurement, and says it lists the figure for its mechanical watches. Aquastar describes it as the full vertical footprint of the case.
Some makers do publish it. Hamilton, Beaucroft and Christopher Ward all list lug-to-lug on their product pages, and Table A below sets their numbers out.
On a lugless design, lug-to-lug equals case diameter. Gnomon gives the Seiko Prospex Tuna as an example, at 49.4 mm for both.
What is lug width on a watch?
Lug width is the distance between the inner edges of a pair of lugs, in millimetres. It sets the strap width the watch takes at the lug end, so a 20 mm lug width needs a 20 mm strap. Measure the inside of the gap, never the outer edges.
Lug width is usually a whole number of millimetres. Hourstriker names 18, 20 and 22 mm as the standard widths, and says 19 and 21 mm are non-standard and limit strap choice. Watch & Strap also notes that some brands use odd sizes, particularly 19 and 21 mm.
Monochrome's Erik Slaven says 20 mm is the most common lug width on men's watches in cases of 37 to 42 mm. BluShark, a strap maker, describes 18 mm as suiting smaller watches and slender wrists, 20 mm as versatile, 22 mm as suiting medium to large watches including many dive and sports models, and 24 mm as suiting larger watches. That is one strap maker's view, not a rule.
If you are weighing a 20 mm strap against a 22 mm one, the watch decides, not taste. The strap has to match the lug width, which the strap section below covers. Table A shows the lug widths published for seven watches, and every one is either 20 mm or 22 mm.
Why lug-to-lug decides fit: case diameter vs lug to lug
Case diameter is how wide a watch is. Lug-to-lug is how long it is along the wrist, and length is what makes a watch overhang. Two watches with the same diameter can differ by several millimetres in lug-to-lug, so diameter alone cannot tell you whether the lug tips will reach past the edges of your wrist.
Aquastar and ODS Jewellers give the same overhang rule: if lug-to-lug is longer than the flat top of the wrist, the lug tips hang over the edges. Keep lug-to-lug at or under the flat top. Our guide to how to measure your wrist for a watch covers finding that width, and it owns the wrist side of the question.
Time+Tide writer Zach Blass argues that, for a wrist, the problem is length rather than width. That is one writer's opinion, and it sits alongside the other views below.
Table A sets out what makers publish for seven watches. The Vannin Field Watch is in it, last, because we are a watch company and want that to be plain. Every figure comes from the maker's own product page, and the fourth column is our arithmetic.
Beaucroft and Christopher Ward label the last column strap width, or strap size, rather than lug width. The three watches of 38 to 38.5 mm other than Vannin run from 43.5 to 48.9 mm lug-to-lug, a range of 5.4 mm. The Field Watch's published 46.0 mm is between the shortest and longest of those three.
Beaucroft's published 43.5 mm is the shortest lug-to-lug of the 38 to 38.5 mm watches in the table, so it is worth a look if lug-to-lug is your priority. It is not the shortest overall: the 36 mm Christopher Ward C63 is shorter, at 42 mm.
Writers and makers also give rules of thumb for lug-to-lug. Table B lists five. They do not agree to the millimetre, and none of them is a standard.
The two guides that give wrist-size bands, ODS Jewellers and Oracle of Time, land at about 46 to 50 mm for wrists of roughly 150 to 180 mm. The other three give a ceiling or a personal limit of around 48 to 50 mm. That reading is ours, and it is a summary, not a standard.
Lug-to-lug is a first filter, not the whole answer. Monochrome's editor Frank Geelen has argued that it does not capture fit by itself, because lug shape, case-back shape and wrist shape also matter. We do not say which row in either table suits which wrist.
| Watch | Case diameter | Lug-to-lug | Lug-to-lug minus diameter (our arithmetic) | Lug width |
|---|---|---|---|---|
| Beaucroft Arc (Teal) | 38 mm | 43.5 mm | 5.5 mm | 20 mm |
| Christopher Ward C60 Trident Pro 300 | 42 mm | 49.3 mm | 7.3 mm | 22 mm |
| Christopher Ward C63 Sealander Automatic (36 mm) | 36 mm | 42 mm | 6.0 mm | 20 mm |
| Christopher Ward C65 Super Compressor | 41 mm | 47.12 mm | 6.1 mm | 22 mm |
| Hamilton Khaki Field Mechanical 38 mm (H69439931) | 38 mm | 47 mm | 9.0 mm | 20 mm |
| NOMOS Club Campus 38 (ref. 735) | 38.5 mm | 48.9 mm | 10.4 mm | 20 mm |
| Vannin Field Watch (coming soon) | 38.0 mm | 46.0 mm | 8.0 mm | 20.0 mm |
| Source | What it says | Wrist reference |
|---|---|---|
| Aquastar (maker) | Lug-to-lug should not exceed the width of the wrist where the watch sits. Many dive watches run roughly 47 to 50 mm, which it treats as the practical ceiling for a wrist under about 50 mm across the flat. | Flat width across the top of the wrist |
| Gear Patrol, Johnny Brayson (personal preference) | Avoids lug-to-lug over 50 mm and prefers 48 mm or less. | His own wrist: 16 cm (6.25 in) around, about 50 mm across the top |
| ODS Jewellers (retailer) | A guide to the longest lug-to-lug by wrist circumference: under 150 mm, up to about 44 mm; 150 to 160 mm, up to about 46 mm; 160 to 180 mm, up to about 50 mm; 180 to 190 mm, up to about 52 mm; over 190 mm, up to about 54 mm. | Wrist circumference in millimetres |
| Oracle of Time, Neil Cody | Under 6.5 in, stay below 47 mm. From 6.5 to 7 in, 46 to 50 mm. At 7 in and over, 50 mm and beyond, especially with curved lugs. | Wrist size in inches, as the source gives it |
| Time+Tide, Zach Blass (personal opinion) | 50 mm or above is a no-go for him. His own sweet spot is around 45 mm for dressy watches and 46 to 48 mm for sporty ones. | His own wrist, which he describes as small |
- ODS Jewellers
- how to measure your wrist for a watch
- Time+Tide
- Beaucroft Arc (Teal)
- Christopher Ward C60 Trident Pro 300
- Christopher Ward C63 Sealander Automatic (36 mm)
- Christopher Ward C65 Super Compressor
- Hamilton Khaki Field Mechanical 38 mm (H69439931)
- NOMOS Club Campus 38 (ref. 735)
- Vannin Field Watch (coming soon)
- Aquastar (maker)
- Gear Patrol, Johnny Brayson (personal preference)
- ODS Jewellers (retailer)
- Oracle of Time, Neil Cody
- Time+Tide, Zach Blass (personal opinion)
- Monochrome's editor Frank Geelen
How to measure lug width and lug-to-lug
Measure lug width across the gap between the inner edges of a pair of lugs, and lug-to-lug in a straight line from the tip of the top lugs to the tip of the bottom lugs. Digital callipers are the most accurate tool. A steel ruler marked in millimetres works if you keep it flat and square to the case.
Measuring lug width
Take the strap off if you can. If you would rather not, measure across the strap immediately below the lugs, at the watch end and not part-way down. Place the callipers or ruler against the inside wall of one lug, close to where the lug meets the case, and read across to the inside wall of the other. Read the figure in millimetres and round to the nearest whole millimetre. Lug widths are usually whole numbers, so a reading near 20 is probably 20, not 19 or 21. If the strap is still on, read its width at the lug end, not at the buckle end.
Measuring lug-to-lug
Put the watch on a flat surface, dial up, with the strap off if you can. Hold the callipers level, so that you read a straight line and not a line that follows the curve of the case. Measure from the tip of a top lug to the tip of the bottom lug on the same side. Repeat on the other side and check that the two readings agree.
The most common mistake is measuring lug width from the outer edge of one lug to the outer edge of the other. That gives a wider figure than the real strap opening, and Watch & Strap and Crown & Caliber both warn against it. Other slips are measuring at an angle, reading case diameter as lug-to-lug, and reading a strap at the buckle end.
You do not need expensive tools. Gear Patrol says digital callipers are not essential but are easier to read, and cheap to buy. Teddy Baldassarre says a simple millimetre ruler will do for lug-to-lug. If a maker does not publish the figure, ask them for it.
Lug shape, short lugs and curved lugs
The same lug-to-lug can sit differently on the wrist depending on lug shape. Curved or downturned lugs follow the wrist, flat straight lugs sit on top of it, and wire lugs or a lugless case keep the length down.
ODS Jewellers says curved or downturned lugs help a longer case sit on a smaller wrist by following the curve. Hourstriker says downward-curving lugs follow the wrist's contour, while flat, straight lugs sit on top and can leave gaps. Davosa notes that early lugs were straight and that case makers later began to tilt them so the watch wraps around the wrist.
Monochrome's Erik Slaven adds that wire lugs tend to have a short lug-to-lug, which is why a 45 mm Panerai Radiomir does not necessarily overwhelm wrists. A lugless case is the extreme: lug-to-lug equals diameter.
Shape is why the numbers are a first filter and photos matter. Look at a watch from the side as well as from above, and read lug-to-lug alongside the maker's own description of the case.
Spring bars, drilled lugs and quick-release straps
A spring bar is a small steel rod with spring-loaded ends that sits between a pair of lugs and holds the strap, as WatchGecko describes it. Drilled lugs and quick-release bars make a strap easier to remove, and fixed bars mean only pass-through straps fit.
Drilled lugs have holes bored right through, so the bar can be compressed and the strap released from outside. Monochrome adds that drilled lugs have become uncommon this century. Gear Patrol notes that you can see from outside that the bars are seated, and Hourstriker says drilled lugs suit people who change straps often.
Quick-release bars have a small pin or lever that you press to release the strap without tools, and they hold on to the bar so it cannot fly off. Watch & Strap says the lever should sit on the underside of the strap, and the bar must lock fully before you wear the watch.
Some watches use fixed bars. Hourstriker describes these as solid bars permanently welded or machined into the lugs, so only single-piece pass-through straps, such as NATO or Zulu styles, will fit. That comes from one source, so read it as how some watches work, not as a rule.
Check how your watch attaches its strap before you order one. Watch & Strap notes that some watches use screws or proprietary systems.
Changing a strap safely
Work over a soft cloth or pad, with the watch face down, so a slip does not mark the case or crystal (Barton Watch Bands). A released spring bar can fly, so take care not to lose it or fling it into your eye (WatchGecko; Gear Patrol). Barton Watch Bands says improvised tools such as razor blades, cards and knives risk scratching the case, so use a proper spring bar tool. Never force a strap between the lugs. Resistance usually means the width is wrong, the bar is misaligned or the strap is too thick for the case design (Watch & Strap). If you are unsure, ask a watchmaker.
These tips draw on guides from Barton Watch Bands, WatchGecko, Gear Patrol and Watch & Strap. None of them replaces the instructions for your own watch.
Which strap fits a 20 mm lug width?
A 20 mm strap, matched at the lug end. Strap width should equal lug width exactly: a strap a millimetre out can leave a gap or need force, so match the number instead of rounding. A 20 mm watch band is a strap that is 20 mm wide where it meets the lugs.
Watch & Strap says many traditional watches take 20 mm straps, field watches among them, but warns against assuming that every watch from one brand shares a size. Case diameter, production year and reference can all change the lug width.
How to size a watch strap comes down to three numbers. Width equals lug width, measured at the lug end. Length is a separate measurement that depends on your wrist, and our guide to how to measure your wrist for a watch covers it. Buckle-end width is the third number.
Strap makers such as Zulu Diver and Holbens write width as two numbers, lug end first. A strap written 22/18 is 22 mm at the lugs and 18 mm at the buckle. Not every strap has a taper: a straight strap keeps the same width throughout, which Holbens says is common on some sport, dive and military-style straps. Check a buckle against the buckle-end width, not the lug width, as Holbens and Watch & Strap advise.
Table C sets out what happens when strap width and lug width do not match, on 20 mm lugs. It draws on BluShark and Watch & Strap. The sources differ, so we give each view.
Width is not the only thing that stops a strap fitting. Watch & Strap points to the thickness of the strap for the case design, the spring bar type and the position of a quick-release lever as well.
Our straps page introduces the future Vannin straps and accessories collection.
| Strap width (on 20 mm lugs) | What sources say | Our note |
|---|---|---|
| 20 mm | Matches the lug width. Watch & Strap says a true 20 mm gap needs a 20 mm strap at the watch end. | The starting point. |
| 19 mm | BluShark, writing about odd lug sizes, says sizing down by 1 mm leaves a small gap on each side that most people barely notice. Watch & Strap says a strap 1 mm out can leave an untidy gap. | About 0.5 mm each side if centred (our arithmetic). Sources differ, and we do not call it fine or wrong. |
| 21 mm | Watch & Strap says it may look close but can need force, which risks the strap edge, spring bars or case. | Do not force it. |
| 22 mm | BluShark says a strap wider than the lug width has to be compressed at the spring bars. That can work with thin, flexible nylon, but is hard or impossible with rigid rubber or tight lug spacing. | Two millimetres wider, so treat it as a different size. BluShark's example is a strap 1 mm wider, and we expect 2 mm to be harder (our reading). |
The Vannin Field Watch's lug numbers
The Vannin Field Watch has a 38.0 mm case diameter, a 46.0 mm lug-to-lug and a 20.0 mm lug width. It is coming soon, so this is the published specification, not a wearing report.
The Field Watch's lug-to-lug is 8.0 mm longer than its diameter (our arithmetic). Table A shows the same difference for six other watches.
Table B's guides are one maker's remark, one retailer's bands and three writers' own views. They are not standards, and we have not set the Field Watch against any of them. We invite you to set the published 46.0 mm beside your own measured wrist, using our wrist measuring guide.
You can see the range on the Vannin Field Watch collection page and register your interest on the Irish Sea Blue page. Our explainer on what a field watch is covers the background.
| Measurement | Published value |
|---|---|
| Case diameter | 38.0 mm |
| Lug-to-lug | 46.0 mm |
| Lug width | 20.0 mm |
| Strap width | 20.0 mm |
| Buckle end | 18.0 mm |
| Strap long side | 120.0 mm |
| Strap short side | 75.0 mm |
| Thickness (including crystal) | 11.2 mm |
| Crown diameter | 6.8 mm |
Frequently asked questions
What is a lug on a watch? A lug is a projection on each side of the case, usually at 12 and 6 o'clock, where the strap or bracelet attaches. A spring bar between each pair holds the strap. The lugs set the strap width, called lug width, and how far the watch reaches along the wrist, called lug-to-lug.
What is lug to lug on a watch? Lug-to-lug is the distance from the tip of the top lugs to the tip of the bottom lugs, the full length of the case. It is not the gap between lugs, and not case diameter. Time+Tide's Zach Blass argues it matters more than diameter, while Monochrome's Frank Geelen says it is not the whole story. The Field Watch's published figure is 46.0 mm.
What is lug width on a watch? Lug width is the distance between the inner edges of a pair of lugs, in millimetres. It sets the strap width at the lug end. Hourstriker names 18, 20 and 22 mm as the standard sizes, and widths are usually whole millimetres. The Field Watch's published lug width is 20.0 mm.
How to measure watch lug width? Take the strap off if you can, or measure across the strap just below the lugs. Measure from the inner wall of one lug to the inner wall of the other, using callipers or a millimetre ruler held flat and square. Never use the outer edges. Round to the nearest whole millimetre.
How to measure lug to lug? Lay the watch flat, dial up, and measure in a straight line from the tip of a top lug to the tip of the bottom lug on the same side, with callipers or a steel millimetre ruler. Repeat on the other side. Check the maker's page first: NOMOS notes that many makers publish only diameter and height, so ask if it is missing.
Case diameter vs lug to lug: which matters more for fit? Diameter is width, and lug-to-lug is length along the wrist, which decides overhang. Same-diameter watches can differ by several millimetres in lug-to-lug (see Table A). Aquastar and ODS Jewellers advise keeping lug-to-lug at or under the flat top of the wrist. Lug shape, case-back and wrist shape also matter, as Monochrome points out.
How to size a watch strap? Match the strap width to the lug width, measured at the lug end, for example by measuring the old strap where it meets the case. Length is a separate measurement that depends on your wrist, and buckle-end width is a third number. The strap's thickness and the spring bar type must also suit the case.
Can you put a 19mm strap on a 20mm watch? A 19 mm strap on 20 mm lugs leaves about 0.5 mm each side if centred (our arithmetic). Sources differ: BluShark calls a 1 mm gap barely noticeable, while Watch & Strap says a strap 1 mm out can look untidy. Wider straps, at 21 or 22 mm, are the riskier direction. Never force a strap.
Prices and specifications checked October 2026. Tell us if something has changed.