How to Size Your Watch Strap

Changing a watch strap is one of the easiest ways to transform how your watch looks and wears. But to get a result that feels “made for you”, you need to get three things right:

• The size of the strap  
• The shape of the watch and your wrist  
• The tools you use to swap it safely

This guide walks through the basics you should understand before you buy and install a new strap.

The Three Essentials

These three factors determine whether a strap physically fits your watch and feels right on your wrist.

1. Lug Width

What it is? The Lug width is the distance between the inside edges of your watch lugs—the “arms” that hold the strap. It is always measured in millimetres (mm). A ruler and trusty google search for your watch model and lug width should enable you to be certain about your lug width. No need for complicated tools.

Lug widths:

• 18 mm, 19 mm, 20 mm, 22 mm are more common
• 16mm, 17mm, 21mm, 23mm, 24mm, 26mm are less common

Why it matters?

Your strap’s width at the watch end must match the lug width:

• 20 mm lugs → 20 mm strap  
• 22 mm lugs → 22 mm strap  

Some description may throw you off. What does a strap that is 20mm to 16mm means? It simply means the strap tapers from 20mm lug width to 16mm at the buckle position.

Too narrow → visible gaps and wobble.  

Too wide → you risk damaging spring bars or the case, and the strap may not seat properly.

2. Wrist Size

Your wrist size is the circumference of your wrist where you wear your watch, measured in cm or inches.

How to measure it?

1. Wrap a soft measuring tape around your wrist where the watch sits.  

2. Note the measurement (e.g., 16.5 cm / 6.5").  

3. If you don’t have a tape:

• Wrap a strip of paper/string around your wrist.  
• Mark where it overlaps. 
• Measure that length with a ruler.

How it affects strap choice?

• Smaller wrist (e.g., 14–16 cm / ~5.5–6.25"): You’ll need shorter straps to avoid the buckle sitting off‑centre or the tail sticking out too far.
• Medium wrist (16–18 cm / ~6.25–7.1"): Standard strap lengths usually work.
• Larger wrist (18–20+ cm / ~7.1–8"+): Look for longer straps (long or XL), or custom lengths.

Your wrist size combined with the watch’s lug‑to‑lug distance (explained later) will tell you what strap lengths you should be looking at.

3. Lug Shape

The shape of your lugs influences:

• How the strap sits against the case  
• Whether you need straight or curved ends  
• How thick the strap can be at the watch end

Common lug shapes:

Straight lugs

• Most common. Strap fits straight across on a simple spring bar.  
• Works with the vast majority of aftermarket straps.

Curved / hooded lugs

• Lugs curve down sharply, or partially cover the strap.  
• Very thick or straight‑end straps may rub the case or not seat properly.  
• Possible customization with manufacturers. 

Integrated lugs

• Strap is visually and mechanically integrated with the case.  
• Often requires proprietary straps or adaptors.  
• Only customized straps will fit.

What to do?

• Look at your watch from the side and head‑on.  
• If the lugs are straight and open, you’re generally safe with standard straps.  
• If they’re very curved, hooded, or integrated, check that the strap’s end shape and thickness will clear the case.

Finer Fit & Comfort

These factors are less about “will it fit” and more about “will it wear beautifully”.

1. Lug‑to‑Lug Distance

What it is? Lug‑to‑lug distance is the measurement from the tip of one lug to the tip of the opposite lug, vertically across the case (top‑to‑bottom when viewed from the front). Measured in mm.

Example:

• Case diameter 36 mm  
• Lug‑to‑lug 46 mm
• Lug Width 18mm

Why it matters? Lug‑to‑lug tells you how much wrist real estate the watch occupies:

• On a small wrist, a long lug‑to‑lug can cause overhang and discomfort. 
• On a larger wrist, a short lug‑to‑lug can feel very compact.

When you combine lug‑to‑lug with strap length, you get the total wrap around your wrist. A very long watch (big lug‑to‑lug) will feel larger on the wrist than a compact one with the same strap length.

2.  Total length

Total length of materials can determined by adding up the Buckle side 75mm, Lug to Lug 46mm and 115mm, long side of the strap.

That is a total of 236mm. Assuming there is an overall of 6mm shown at the yellow zone, that is still a total length of 230mm materials. That sounds way too long if you have an 180 mm or 7” wrist size?

No. So where did the 50mm difference go to?

We lose about 20 mm of the total length from the turns around the wrist and buckle. But the biggest difference is the overlap of the straps. The thicker the strap, the shorter they wear.

3. Wrist Shape

Two people with the same wrist circumference can have very different wrist shapes:

• Thicker Outer Wrist
• The larger the outer wrist vs inner wrist, the longer buckle side and shorter long side strap is required to centre the buckle.  Eg. A 180 mm wrist with this shape may need 85mm + 115mm lengths instead of 75mm + 115mm.
• More balanced both sides.
• If both inner and outer wrist are closer in thickness, the standard lengths should sit comfortably.
• Individual wrist.
• All of our wrists are as unique as our thumb prints. Experience and understanding strap materials and thickness can help getting the right lengths.

3. Buckle or Clasp

The closure you use also influences both sizing and comfort.

Common types:

Standard tang buckle  

   - Classic pin and hole.  

   - Works with most leather, canvas, rubber and textile straps.  

   - Multiple holes allow fine adjustment.

   - Buckle side to Long side ratio about 3 : 5 or 75mm : 115mm

Deployant Butterfly clasp  

   - Buckle width to match narrower end width of watch band

   - Buckle side to Long side ratio about 3 : 5 or 75mm : 115mm

Deployant Single Fold clasp

   - Buckle width to match narrower end width of watch band

   - Buckle side to Long side ratio about 1 : 1 or 100mm : 105mm

What to check:

• Buckle width: If you want to reuse an original buckle or clasp, match the strap’s buckle end width (e.g., 18 mm).  
• Strap thickness at buckle: Ensure it fits under the clasp and through the keepers.

Tools Required

Using proper tools makes strap changes faster and reduces the risk of scratching your case or bending spring bars.

Spring Bar Tweezer Tool

A tweezer‑style tool that grabs both ends of the spring bar concurrently.

• Excellent for bracelets and tight tolerances.  
• Compresses the bar evenly and lifts it straight out.  
• Very helpful on watches with solid end‑links or small clearances.

Spring Bar Fork (Strap Change Tool)

The classic tool for strap changes:

• One end has a forked tip.
• The other end is often a small pin.

Using the fork:

1. Insert the fork between strap and lug.  
2. Hook the inner “shoulder” of the spring bar.  
3. Pull inward to compress.  
4. Slide or lift the strap out of the lugs.

Ideal for most:

• Leather
• Canvas / nylon  
• Rubber / silicone style straps

Spring Bar Pin

Useful when your watch has drilled lugs (small holes on the outside of the lugs):

1. Place the pointed pin into the lug hole.  
2. Press inward to compress the spring bar.  
3. Gently lift the strap or bracelet out.

Many strap tools combine fork and pin ends into one double‑ended tool.

Wrist Size and Suggested Strap Lengths

Strap length is usually written as long part + short part (excluding the buckle), e.g., 120/75 mm.

The table below combines:

• Wrist size
• Typical lug‑to‑lug distance
• Wrist shape notes
• Suggested strap lengths
• Example RSM collections that typically work well for that range.

General tolerance

• You usually have 5–10 mm of leeway:
• A strap that’s slightly longer/shorter can still work as long as you’re not on the very first or last hole.
• Thicker straps (canvas, padded leather) behave “shorter” on the wrist because they don’t conform as tightly. If you’re between sizes and prefer thicker materials, consider the longer option.

Putting It All Together: Changing Your Strap Step‑by‑Step

1. Confirm lug width  

• Measure between lugs or check specs (e.g., 20 mm)
• Choose a strap with that same width at the watch end

2. Check wrist size and strap length  

• Measure your wrist.  
• Use the table to pick an appropriate length (e.g., 115/75 or 120/75).

3. Assess lug shape and lug‑to‑lug  

• Straight lugs → most straps fit.  
• Curved/hooded → avoid overly thick or stiff straps at the watch end.  
• Longer lug‑to‑lug on a small, round wrist → favour slightly shorter, more flexible straps.

4. Decide on buckle or clasp  

• Reuse original buckle? Match the buckle width (e.g., 18 mm).  
• Using a deployant or aftermarket clasp? Check that strap thickness and taper are compatible.

5. Prepare tools and workspace  

• Have a spring bar fork (and pin or tweezer if needed).  
• Work over a soft cloth to avoid scratching the case or losing spring bars.

6. Remove the old strap  

• Use the fork or pin to compress the spring bar.  
• Carefully lift the strap out from between the lugs.

7. Install the new strap  

• Insert spring bar into the strap.  
• Seat one end into a lug hole.  
• Compress the other end with the tool and guide it into the opposite lug.  
• Gently tug the strap to ensure the bar has clicked into place.

8. Final comfort check  

• Strap should sit flush between the lugs with no gaps or forcing.  
• Buckle should sit roughly in the centre underside of your wrist.  
• You should have some adjustment holes available in both directions.