The first thing to get right with a watch strap loop is its width. This is the inside width of the little loop, and it must match the width of your strap: a loop that is too narrow simply won't slide on, while one that is too wide will twist around the strap and let the free end lift away. The good news is that this measurement takes a matter of seconds, and you don't need any watchmaker's tools.
What you will need
An ordinary ruler marked in millimetres is all it takes. Pick one that is thin and easy to read: a steel rule or a clear school ruler is ideal. A dressmaker's tape measure will do at a pinch, but it twists easily and the reading is less clear. Lay the watch flat on a table, dial facing up, and work in daylight.
Where should you measure the strap?
The loop sits around the strap just after the buckle, so that is where the measurement matters, along with the point where the strap meets the lugs of the case:
- At the lugs: measure the strap where it attaches to the case, from one edge to the other. On most watches, this is the strap's reference width (18, 20 or 22 mm, for example).
- At the buckle: measure the strap right next to the buckle, where the old loop used to sit. This is the most reliable measurement, as it is exactly where the new loop will go.
Line up the zero on the ruler exactly with one edge of the strap and read the value at the opposite edge, looking straight down from above. Round to the nearest millimetre: strap loops are chosen to the millimetre, from 10 mm for slim straps to over 30 mm for wide ones.
Loop width = strap width
The rule is simple: if your strap measures 20 mm, choose a 20 mm loop. The width given for each loop is its inside opening, in other words the width of the strap it takes. There is no need to add any allowance: a correctly sized loop should slide on with slight friction and no play.
If you still have the old loop, even a broken one, you can measure its inside width to double-check your reading. If the two values differ, go by the strap: an old loop may have lost its shape over time.
Straps that taper
Many straps, particularly leather ones, are wider at the lugs than at the buckle. A strap that is 20 mm at the case end may therefore be only 18 mm at the buckle end. In that case, it is the width near the buckle that counts, because that is where the loop sits. Measure the strap on the section where the loop will go, just after the buckle, and choose that width.
If your measurement falls between two sizes, go for the one closest to the actual width where the loop will sit. A silicone loop, being more flexible, will forgive a slight difference; a steel or leather loop calls for greater accuracy.
Smartwatches: go by the model
Smartwatch straps often have a distinctive shape, and some loops are designed for one specific model. For a Garmin, Samsung, Huawei, Xiaomi, Amazfit, Suunto, Polar, Fitbit, Kospet or Casio G-Shock watch, the safest approach is to start from the exact name of your model rather than a ruler measurement. Two watches from the same brand may well use different widths: at Garmin, for instance, a Forerunner 935 takes a 22 mm strap, whereas a Fenix 5X takes a 26 mm strap.
The model name is usually shown on the back of the case, in the watch's companion app or on the watch's packaging. Then look for the loop made for that model: that way you can be sure of getting the right width and the right shape.
Summary
- Measure the strap with a ruler marked in millimetres, from one edge to the other.
- Go by the measurement taken right next to the buckle, where the loop sits.
- Choose a loop of the same width as the strap, to the millimetre.
- For a smartwatch, start from the exact model name.
Once you know the width, all that remains is to choose the loop's material: see our guide Choosing the material for your strap loop, then the guide Replacing a watch strap loop for fitting.