Why a Watch's Size on Paper Doesn't Tell You How It Will Fit

Quick answer: A watch's case diameter doesn't tell you how it will fit. The most important measurement is lug-to-lug length, which should be no wider than the flat top of your wrist. Thickness, bezel width, dial colour and the strap or bracelet all change how big a watch looks and feels.

You've found a watch listed at 40mm, exactly the same as one you already own, so it should fit the same. Then it arrives and feels completely different. This happens all the time, because diameter is just one number. In this watch size guide I'll explain the measurements that really matter and how to choose the right watch size for your wrist.

Diameter is usually measured across the case, excluding the crown. But brands measure differently, and two watches with the same diameter can have very different shapes, lug lengths and bezels. A 40mm dive watch with a chunky bezel and long lugs can wear far larger than a 40mm dress watch with short, curved lugs.

This is the distance from the tip of the top lugs to the tip of the bottom lugs. If it's longer than the flat top of your wrist, the lugs will overhang the edges, making the watch look too big, however modest the diameter.

A slim watch under about 10mm slides easily under a shirt cuff and sits close to the wrist. Thicker watches, often 13mm or more for dive and chronograph models, sit taller and feel heavier.

A wide bezel shrinks the visible dial, making a watch look smaller. A thin bezel with a large dial opening makes a watch look bigger than its diameter suggests.

Light dials such as white, cream and silver tend to look larger. Dark dials such as black, navy and green tend to look smaller and more compact.

A bracelet that tapers towards the clasp makes a watch feel more elegant. Soft leather and fabric straps hug the wrist, while stiff straps and solid bracelets can make a watch sit higher.

1. Wrap a soft tape measure, or a strip of paper, around your wrist just above the wrist bone.
2. Note the circumference in centimetres or inches.
3. Now measure the flat top of your wrist from edge to edge with a ruler. This is the key number for lug-to-lug.
4. Choose watches with a lug-to-lug measurement equal to or slightly less than that flat width.

Use these ranges as a starting point rather than a rule:

• Wrist up to 15cm (about 6in): 34mm to 38mm cases, lug-to-lug up to about 44mm.
• Wrist 15cm to 18cm (6in to 7in): 38mm to 41mm cases, lug-to-lug about 44mm to 48mm.
• Wrist over 18cm (7in plus): 41mm to 44mm cases, lug-to-lug about 48mm to 52mm.

Personal style matters too: plenty of people with larger wrists love the vintage look of a smaller watch, and vice versa.

• Look up the full specifications: diameter, lug-to-lug, thickness and lug width.
• Compare them with a watch you already own and like the feel of.
• Print a paper template to scale and try it on your wrist.
• Look for wrist shots from owners with a similar wrist size.
• Buy from retailers with fair returns and free bracelet sizing.

Most men find 38mm to 42mm comfortable, but the right size depends on wrist size and lug-to-lug length rather than gender.

Not for most wrists. A 40mm watch with a lug-to-lug under about 48mm fits a wide range of wrists comfortably.

Snug enough not to slide around, but loose enough to slip one finger underneath the strap. The lugs shouldn't hang over the edges of your wrist.

Getting the size right is one of the biggest factors in whether you'll love wearing a watch. Check lug-to-lug and thickness, not just diameter, and try before you buy whenever you can. If you're choosing your first watch, my guide on how to choose your first proper watch puts sizing alongside the other key decisions.