Watch Strap Size Guide: Three Measurements, Ten Minutes, No Returns
Strap sizing is three separate numbers: the lug width, the strap length and your wrist. Most wrong orders get one of them right and assume it covers the other two.
Most people think a watch strap has a size. It has three. The gap between your lugs decides whether the strap fits the watch. The length of the two pieces decides how far it reaches. Your wrist decides whether any of it is comfortable. Get all three before you order and you won’t be writing to us about a return. Get one and guess the rest, and you will.
I sell straps for a living, so I’d like you to hear this from the other side of the counter: a correct measurement costs nothing, and a wrong strap costs you a week and some postage. This guide takes the three in order and then shows you how to read the labels on our own straps.
Lug width: the one that can’t be wrong
Lug width is the distance between the inside edges of the two lugs, the little horns that stick out of the case, where the spring bar sits. It’s quoted in millimetres, and it’s the number printed on the strap as “20mm” or “22mm”. If the strap is the wrong width, nothing else matters, so measure this first.
To do it, take your watch off and put it face up on a towel. Lay a steel rule, or better a pair of calipers, across the gap between the lugs at the spring bar. Read the number to the nearest millimetre. If you’re between two sizes, measure again and measure somewhere else on the case, because lugs aren’t always parallel.
Measure the lugs, not the old strap. A strap tapers from the lugs towards the buckle, so the width printed on the buckle end is smaller than the lug end, and a worn strap can lie to you in both directions.
A few widths you’ll see in our shop: MoonSwatch is 20mm, and our Tudor Ranger straps are 20mm. Our cut-to-size FKM strap comes in 18, 19, 20 and 22mm. Those are the strap widths on our own product pages. For the lug width of any particular watch, check the case or ask us, because I’m not going to guess it for you.
20mm or 21mm: why one millimetre is a big deal
A 20mm strap in 21mm lugs leaves a gap of about half a millimetre each side. That’s general guidance rather than anything we’ve tested on a specific watch. It looks sloppy and it lets the strap shuffle on the spring bar. A 21mm strap in 20mm lugs won’t go in at all without squeezing the edges, and I wouldn’t try. If you’re stuck between sizes, buy the width that matches your watch and ask us about the odd one out. Odd sizes like 19mm and 21mm are where people most often get caught, because they sit so close to the common ones.
Strap length: the long piece and the short piece
Most straps are two pieces. The buckle piece is normally the shorter one, and the piece with the holes is the longer. That’s the general convention. On our own labels the numbers are written as two lengths, such as 105/100 or 120/75.
The length that matters isn’t the total on the box. It’s the length that wraps your wrist with the watch on it, and a thick watch, a deployant clasp or a chunky case all change that. This is why we also list a wrist range on our straps, and I’d trust the wrist range over any number you work out yourself.
Your wrist: the number that decides everything
This is the measurement you’ll actually do at home, and we have a separate page for it: how to measure your wrist. The short version is a soft tape measure around your wrist just above the wrist bone, snug but not tight, so you can slide a finger underneath. No tape? A strip of paper or string works the same way. Mark the overlap, lay it flat and measure it against a ruler.
Measure where the watch sits, not where you wish it sat. Allow roughly a finger’s width, 1 to 2cm, for comfort. If you’re between two sizes, go larger. A strap that’s slightly loose is irritating, but one that’s too tight is something you’ll stop wearing.
How to read our labels
Our strap variants carry a label such as Standard (105/100) with a wrist range. Here are the ones we use, taken straight from our own product pages.
| Strap | Our label | Wrist range |
|---|---|---|
| Woven nylon NATO (Tudor Ranger) | One Size | Fits up to 24cm |
| Tudor Ranger sailcloth with deployant | Standard (105/100) | 18.0cm to 21.5cm |
| Tudor Ranger herringbone tweed | Standard (120/75) | 17.0cm to 20.5cm |
| Cut-to-size FKM with deployant | Standard (106/106) | 18.7cm to 22.2cm |
What to take from it: the wrist range is the part to read. The pair of numbers in brackets is the construction, and the range beside it is the promise. Pick your strap from the range, and use the lug width to decide which model it’s for.
If you’re at the very small or very large end, a NATO is the forgiving choice, since it’s a one-size strap with a wide range. If you want something with a clasp, our cut-to-size FKM straps trim from both sides to your wrist. Our deployment FKM strap comes in 18, 19, 20 and 22mm, and the MoonSwatch version is 20mm. Yes, we make these. No, a cut-to-size strap isn’t automatically right for you. If your wrist is outside the printed range, email us before you order.
When to ask first
If the watch is old, odd or aftermarket, ask. If the lugs are drilled, or the lug-to-lug distance is long, or the case is thick, tell us the model and we’ll say what fits. If you have an old strap you like, measure it at the lug end rather than guessing. That is quicker than a return.
For MoonSwatch sizes and how to change the strap, our MoonSwatch strap replacement guide covers it properly. Clasp questions live in our deployant strap guide, and I won’t repeat them here.
The ten-minute checklist
Do these in order, and write the numbers down. First, measure the lug width and note it in millimetres. Second, measure your wrist with a soft tape where the watch sits. Third, look at the wrist range on the strap you like and check your number falls inside it, not on the edge. Fourth, check the strap is listed in your lug width, because a strap in the wrong width is a return waiting to happen. Fifth, if anything doesn’t line up, ask before you order. It takes us a minute to answer and it saves you a fortnight.
I’d do it with the watch on the wrist, in daylight, with a mug of tea. It’s dull, but it’s the only part of buying a strap that is entirely under your control.
Where to go next
When you know your three numbers, the straps sorted by watch are in the Tudor, Omega and MoonSwatch collections, and everything is in all watch straps.
Three numbers. Ten minutes. Then buy the strap.
Frequently asked questions
What does 20mm mean on a watch strap?
It’s the strap’s width where it meets the watch, and it must match the gap between your watch’s lugs. A 20mm strap suits 20mm lugs.
Will a 20mm strap fit 21mm lugs?
It will sit in them, but with a gap on each side and some movement on the spring bar. We’d buy the strap that matches the lug width.
How do I measure lug width?
Take the watch off, then measure the gap between the inside edges of the lugs at the spring bar with calipers or a steel rule. Round to the nearest millimetre and measure again if you’re between two sizes.
How do I know my strap length?
Start with your wrist. Measure it with a soft tape just above the wrist bone, then choose a strap whose printed wrist range includes your number. Allow 1 to 2cm for comfort.
How long should a watch strap be?
Long enough to wrap your wrist with a finger of room to spare. We list a wrist range on our straps, so pick the one that includes your measurement rather than working out the length yourself.
What if my wrist is outside the listed range?
Email [email protected] before you order. A NATO or a cut-to-size strap may be the better answer for your wrist.