How to Measure Your Watch Strap Size
Your strap size is the lug width: the gap between the lugs, in millimetres. Here's how to measure it in under a minute with the on-screen ruler below, a printed ruler, or calipers.
What you're measuring
Lug width is your strap size
The gap between the lugs, where the strap attaches. It's the only number you need to buy a strap: a 20mm gap takes a 20mm strap. Measure it inside edge to inside edge.
How wide the case is. It's the size watches are sold by, but it doesn't tell you the strap size: 40mm watches take 18, 20 or 22mm straps depending on the model.
Tip-to-tip length of the case. It decides how big the watch wears on your wrist, not which strap fits. Check it against your wrist →
- Calibrate. Hold a bank card flat against the screen and drag the slider until the dashed box matches the card's width.
- Measure. Lay the watch face-down and drag the gold markers to the inside edges of the lugs.
- Read. The number is your lug width: the strap size to buy.
Hold any bank/credit card flat against the screen and drag the slider until the dashed box matches the card's width exactly.
Drag the two gold markers to the inside edges of your watch's lugs. The reading is your lug width.
Three other ways to measure lug width
- Calipers (most accurate). Close the inside jaws between the lugs, at the spring bar, and read to the nearest 0.1mm. Most watches measure within a few tenths of a whole number.
- A millimetre ruler. Lay the watch face-down, put the ruler across the lugs and look straight down. Read from the inside edge of one lug to the inside edge of the other. No ruler? Print our true-size ruler and lug-width gauge.
- The strap you already have. Measure the strap's width right where it meets the watch, not at the buckle end, which is often narrower.
Measuring strap length
Width is what has to match; length is about comfort. Two-piece straps are listed as two numbers, such as 120/75mm. To size a replacement, measure each half of a strap that fits you, from the spring bar to the far end (on the buckle half, stop where the strap ends, not at the buckle tip). To start from scratch, measure your wrist and use the strap length calculator.
Common mistakes
- Measuring the outside of the lugs. That includes the lugs themselves and gives a reading 4–8mm too big.
- Using the case diameter. A 40mm case doesn't mean a 20mm strap; lug width only averages about half the case size.
- Rounding an odd reading to an even size. A watch that measures 21mm takes a 21mm strap. Never buy wider; a size narrower fits with a small gap.
- Measuring a tapered strap at the buckle. Only the lug end has to match the watch.
Lug width vs lug-to-lug
Lug width is the strap width you buy. Lug-to-lug is the tip-to-tip length of the case, which decides how big the watch wears — it doesn't affect strap size.
Common strap sizes
Dress watches are typically 18–20mm, divers and sports watches 20–22mm. Odd sizes (19mm, 21mm) exist and are worth double-checking before you buy. See the watch strap size guide and chart.