How to Measure Your Wrist Size

Getting the right watch strap fit starts with one accurate measurement. This guide covers how to measure your wrist size using nothing more than a piece of string and a ruler, how to interpret that number against standard strap sizing, and the small but common mistakes that can throw off an otherwise straightforward process.

Why wrist size matters when choosing a watch strap

Getting a watch strap to fit correctly starts with one simple number: your wrist circumference. Without it, you’re guessing. And an ill-fitting strap makes itself known quickly. Too tight, and it pinches the skin and restricts movement. Too loose, and it shifts around, pulls the watch face off-center, and lets the buckle dig in at awkward points throughout the day.

Knowing how to measure your wrist size has nothing to do with fitness or aesthetics. Think of it the same way you’d measure your waist before buying a belt — it’s just a practical starting point. That measurement tells you which strap length will give you a secure, comfortable fit, with the buckle closing in the middle holes, right where it’s designed to sit.

Most watch straps are sized in millimeters and come in standard lengths with several adjustment holes. Getting your wrist circumference right means you can match your size to those ranges before you buy, rather than discovering the fit is off once the strap arrives.

There’s another benefit worth mentioning: it gives you a more accurate sense of how a watch will actually wear on your wrist. A larger case sits and looks quite different on a narrower wrist than on a broader one, and knowing your measurement helps you factor that in when choosing a watch.

If you’re already in the research phase, it’s worth browsing Marathon’s watch straps alongside this guide to get a feel for the sizing options available.

The easiest way to measure your wrist with a string and ruler

You don’t need a tailor’s tape measure to get an accurate wrist measurement. A piece of string, a thin strip of paper, or even a length of ribbon works just as well, and the whole process takes less than two minutes.

1. Cut or tear a piece of string or paper strip long enough to wrap comfortably around your wrist with a little extra to spare.
2. Wrap it snugly around your wrist. Tip: measure where your watch actually sits, typically just below the wrist bone. Measuring at the bone itself can add a few unwanted millimeters and leave you with a strap that feels loose during wear.
3. Pinch or mark the point where the string overlaps. Don’t tie it. You’re capturing the circumference, not creating a knot.
4. Lay the string flat against a ruler or straight edge.
5. Read from the starting end to your marked point. Note the result in both inches and millimeters before you do anything else.
6. Repeat once or twice to confirm consistency. Small variations in tension can nudge the number slightly, so averaging two readings gives you a more reliable result than relying on one.
7. Write it down. A measurement you’re trying to hold in memory has a way of disappearing the moment you open a new browser tab.

Recording your wrist circumference in both units is worth the extra second. Strap sizing references aren’t standardized, and some watch band size guides list widths in millimeters while others use inches. Having both on hand means you’re covered either way. If you want to skip the improvisation entirely, a proper sizing gauge from our watch tools collection gives you a clean, accurate reading with no guesswork involved.

How to read the measurement for strap size

Once you have your wrist circumference, you have a solid starting point. But the number alone doesn’t tell the whole story. The bulk and thickness of your watch case also affect how a strap sits on your wrist, so it’s worth thinking about both together.

1. Identify your size range. Most strap sizing guides group wrist measurements into small, medium, and large. Under 165mm is generally small, 165mm to 190mm is medium, and above 190mm is large.
2. Account for case thickness. A thicker case raises the watch higher off the wrist, which can make a strap feel tighter than the measurement suggests. If your watch has significant case bulk, a slightly longer strap may be more comfortable.
3. Aim for the middle adjustment hole. A good fit means buckling at or near the center hole, leaving room to tighten or loosen as needed.
4. Check for comfort, not just fit. You should be able to slide one finger underneath the strap without forcing it. It should lie flat without pinching the skin at either edge.
5. Match strap width to your lug width. Once you know your wrist size, browsing by lug width is a practical next step. If your watch takes a wider strap, 22mm watch straps are a good place to start narrowing things down.

Note: Material matters too. A rubber strap and a leather strap at the same measured length can feel quite different on the wrist, so treat your measurement as a guide rather than a guarantee.

The goal is a strap that sits flat, allows about a finger’s width of slack, and doesn’t pinch. That combination will serve you better than chasing an exact number.

Common mistakes to avoid when measuring your wrist

Small errors in technique are easy to make and just as easy to avoid. Knowing where people typically go wrong makes the whole process faster and gives you a measurement you can trust.

• Pulling the string or tape too tight. Snug is correct; compressing the skin is not. Too much tension reads shorter than your actual wrist circumference, which can lead to a band that sits uncomfortably tight.
• Measuring over a sleeve. Even thin fabric adds millimeters. Always measure directly against bare skin.
• Measuring at the wrong time of day. Wrists can swell slightly in heat or after exercise. Measuring in the morning, at rest, gives you the most consistent baseline.
• Rounding too aggressively. A few millimeters matter when it comes to strap sizing. Write down the precise figure before you consult a wrist size chart.
• Confusing wrist circumference with band length. They’re not the same number. Circumference tells you your wrist size; band length accounts for the buckle, taper, and overlap built into the strap design.
• Stopping at circumference. A well-fitting watch also depends on lug width. Once you have your wrist measurement, it’s worth taking a moment to measure your watch lug width too.

None of these take long to get right. A clean, repeatable measurement takes under a minute and gives you a result you can use with confidence.

What to do after you know your wrist size

Once you have your wrist circumference, the next step is simple: use that number to compare strap options against a watch band size guide before you buy.

Most straps are sized by lug width, typically 18mm to 22mm, but fit also depends on strap length. Standard straps generally come in short, regular, and long to cover different wrist circumferences. If your measurement falls between sizes, go up rather than down. An earlier buckle hole is an easy adjustment; a strap that’s too tight is not.

Marathon’s strap sizing is built around practical use, with options designed to work across a realistic range of wrist sizes. Knowing your wrist circumference means you can check compatibility with confidence rather than guessing from a product photo.

One more thing worth confirming before you order: lug width. A strap can be the right length for your wrist and still not attach properly if the width doesn’t match your watch case. If you’re replacing an existing strap, check that measurement too.

The process is straightforward once you have a number to work with. Measure first, then compare. You’ll move through strap selection with a clearer sense of what fits, and a lot less second-guessing.