Watch Band Size Calculator
Find your watch strap length and lug width from your wrist and case size, with a comfort allowance so the watch sits snug but not tight.
How it works
Strap length = wrist circumference + comfort allowance (5/10/15 mm) · Lug width ≈ case diameter ÷ 2, rounded to the nearest even mm
Two numbers size a watch band. The total strap length is your wrist circumference plus a small allowance so the buckle fastens comfortably with holes to spare. The lug width — the gap between the lugs where the strap attaches — runs close to half the case diameter and comes in even sizes like 18, 20 and 22 mm; get this exact or the strap will not fit.
Worked example
A 175 mm wrist worn at a regular fit needs about a 185 mm strap. A 40 mm case has lugs around 20 mm apart, so you would order a 20 mm strap — the most common size for mid-sized watches.
Frequently asked questions
How do I measure lug width?
Measure the distance between the inner faces of the two lugs where the spring bar sits, in millimetres. It is almost always an even number: 18, 20, 22 mm and so on. The strap must match this exactly.
Is lug width really always half the case size?
It is a close rule of thumb, not a law. Many 40 mm watches use 20 mm lugs, but designs vary, so confirm by measuring your watch or checking the spec before buying a strap.
What if my wrist is between strap holes?
Pick the fit that lands the buckle near the middle of the holes so you can tighten or loosen through the day. Metal bracelets are sized by removing links rather than holes.
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This calculator is for educational purposes. Double-check important results before acting on them.