OPTO WATCH CO. | How to measure your strap size?

Choosing the right watch strap starts with one simple step: measuring the lug width. Here's a quick guide to help you get it right every time.

1. What Is Lug Width?

Lug width is the internal distance between the lugs — the two protruding arms that hold the strap. It’s measured in millimeters and determines what strap size will fit your watch.

2. How to Measure Lug Width?

Use a digital caliper or a precise ruler for accuracy. Always measure from the inside of one lug to the inside of the other — not from the outer edges.

3. Common Lug Widths

Typical lug sizes include:

• 18mm

• 20mm

• 22mm

Some watches may have less common sizes like 19mm or 21mm — which is why measuring is essential.

4. What About Proprietary Lug Systems?

Certain brands use custom lug designs that only work with their own straps. These systems prevent you from using standard straps. Examples include:

• Apple (Apple Watch)

• Audemars Piguet (Royal Oak)

• Richard Mille

Always check if your watch uses a proprietary system before buying a new strap.