Start with the lug width
The lug width is the space between the two attachment points on your watch case. Measure it in millimetres with a ruler or calliper. A strap should match this width.
Check the length
Measure your current strap without the buckle. Compare its two halves with the dimensions listed on the product page. Wrist size alone does not tell the whole story; the size of the watch case also affects fit.
Check the attachment
Some watches use proprietary attachments or curved ends. Check your watch manufacturer’s specifications before ordering. If you are unsure, contact the store before purchase.