Case Diameter

Most of the time when we talk about the size of a watch the measurement we talk about is the case diameter, which is the full width of the case excluding the crown and any pushers.

The case diameter is an extremely important measurement, one that is often discussed amongst the watch community. As trends and fashion have changed, case diameter has altered drastically over the years; in the 1950's for example, the most popular size of a men's wristwatch was 34mm, compared to the most popular size today being 42mm.

The perfect watch diameter for you depends not only on your wrist size, but also the style of watch, I myself have a range of timepieces, varying from a 26mm up to 42mm. I am part of the growing community that is ever searching for the perfect size watch, you'll find a vast number of blog posts discussing 39mm being the 'best' dive watch size, while others, like myself, prefer a smaller 36mm, also known as mid-size.

When in the market for a new watch, it's important to try on a watch if you are able to. Watches are immensely personal items and finding a watch that suits your wrist size and style is a cathartic experience.

Lug-to-Lug

The full length of the watch case from the top lugs down to the bottom is known as the lug-to-lug length.

The measurement can lead to what the watch community calls watch 'wear size', for example, if we compare a Longines Skin Diver to an Omega Speedmaster; although both watches have a 42mm case diameter and similar case height (see below), they vary drastically in lug-to-lug distance. The Skin Diver has a lug-to-lug of 52.5mm, whereas the Speedmaster is only 47mm. This leads to the Speedy 'wearing' smaller than the Skin Diver.

Lug-to-lug distance also plays a large role in buying a new watch strap as it is this measurement along with your wrist size that dictates the length or the strap needed.

The smaller your lug-to-lug distance, the longer the strap will need to be to fit around your wrist, in the same way that a longer lug-to-lug distance would lead to a need for a shorter strap. We’ll learn more about how to measure both wrist size and the lug-to-lug distance below.

Case Height

Lastly, we have the case height, or thickness. This is the measurement from the base of the watch to the top of the glass when viewed from the side. This is a measurement that is often overlooked when shopping for a watch as most watches have a case height in proportion to their overall size and function.

For years watch companies have been vying for the top-spot by creating the thinnest watch, a title currently held by Bulgari with their Octo Finissimo Ultra COSC, measuring a mere 1.70mm thick. The other end of the scale would be watches designed for extreme deep sea exploration, like the Rolex Deep Sea Challenge measuring 23mm thick, and that isn't even the chunkiest watch out there, with Invicta making a 29.5mm watch, ironically, a homage to the Deep Sea Challenge.

The case height is another measurement that doesn’t play a huge role in purchasing a new strap as most watches would suit various strap thicknesses. If you own a thinner watch, avoid fitting a strap that's thicker than the watch itself. Similarly, a thick strap will look out of place on watches with thin lugs.

The most important strap measurement.

To begin, simply measure the inside distance between the two lugs, where the strap meets the watch. There are several methods in doing this.

A Ruler:

A ruler, scale, or line gauge, although not as accurate as other methods, is the most common method because it is a device we all have. Make sure the ruler you use is accurate and has measurements in millimeters.

A Watch Strap and Lug Measuring Ruler:

A tool designed specifically to measure watch straps and lugs, it consists of various notches, from 6mm to 30mm. The notches are used to place into the lugs of a watch to find out the lug width, simply find the notch that fits your watch with no movement.

A set of Callipers:

Callipers, especially digital callipers, are the most accurate way of measuring your watch, use in the same way as a ruler making sure to measure the inside of distance of the lugs.

Things to remember when measuring the lug width:

Measure the Inside.

The lug width is the inside measurement of the two lugs, not the outside.

Have an odd Lug Width?

If you find your lug width isn't to the exact millimeter, you may have a more uncommon lug width. This is not an issue, many watches, like the TAG Heuer Aquaracer and Blancpain Fifty Fathoms, have lugs that are 20.5 and 22.5 respectively. This means you are less likely to find a strap that is a perfect fit, in this situation, the best option is to size either up or down depending on the material of the strap, leather, rubber and fabric straps will most likely fit sized down, eg. a 21mm strap is likely to fit a 20.5mm lug. Whereas steel bracelets will not size down and sizing up is best. An alternative is to buy a steel bracelet with an adjustable lug width. Whatever you choose, its often best to use the spring bars that came on your watch.

Check your Strap.

If you're struggling to measure your lug width, another simple way to find it is to check the strap that is currently fitted to the watch. Many manufacturers print or stamp the size directly on the back of the strap. If their are two sizes printed, you are most likely looking at the buckle width too, eg. 22/18 printed on the back of a straps means the lug width is 22mm, and the buckle width is 18mm.

The Full Length of your Timepiece.

What is the lug-to-lug-distance?

Measuring the lug-to-lug distance can be done in the same way as the lug distance, either with a ruler or with callipers. Being accurate whilst measuring the lug-to-lug distance is less important than with the lug width, but the more accurate you can be will lead to a more accurate sizing of the strap.

A Ruler:

Simply hold the ruler against the watch and make a note of the overall length from top to bottom.I prefer a wooden or plastic ruler to avoid scratching the watch. As an extra precaution, I also always measure from the back to protect the watch crystal.

A set of Callipers:

Measuring the lug-to-lug distance with callipers, will give the most accurate reading of the measurement. As many callipers are made of metal and are often quite sharp, it's important to be careful not to scratch the lugs of the watch, if you are worried about this, a simple method is to cover the ends of the lugs with painter's tape, this will protect the lugs from marks, without leaving any residue on the watch afterwards.

Things to remember when measuring the Lug-to-Lug:

Check your Spring Bars.

The lug-to-lug is the measurement used to give an accurate reading of what watch strap length you will need. However, if you have a watch with a large distance between the lugs and the spring bar holes, it can be beneficial to measure the distance between the spring bars too.

A Hamilton Khaki Field, for example, has a lug-to-lug of 47mm, and a spring bar distance of 46mm due to how close the spring bars are to the end of the lugs, this distance wouldn't make a difference with strap length so either measurement is fine. Whereas an Rolex Milgauss has a lug-to-lug of 49mm, and a spring bar to spring bar distance of 42mm, this 7mm distance could make a difference in the strap size you choose so taking both measurements is often best.

Want a Strap for Multiple Watches?

Purchasing a watch strap to fit multiple watches is a common occurrence, I myself have 4 watches that I often swap and change straps on. The important thing to note here is that as long as the lug width is the same, the strap will fit each watch, however, due to the different lug-to-lug distances you may be on a different strap hole per watch.

Want to keep your buckle?

If your current strap has a clasp or a buckle that you would like to move over to the new strap, you will also need to measure this.

Measuring your buckle or clasp.

Measuring your clasp or buckle is just as easy as measuring your lug width, the best method and tool to use is a Watch Strap and Lug Measuring Ruler as this will give you an accurate measurement. Simply measure the inside distance where the strap meets the buckle or clasp.

Clasp compatibility.

If you have a watch with a clasp, you will need to make sure of a few important factors before purchasing a new strap.

Make sure the clasp you are hoping to use is compatible with the strap you would like as many clasps are designed for specific styles of watch strap. Standard sports deployment and pusher clasps are likely to fit most standard straps, as they are found on various watch brands.

Don't forget the holes:

If you are hoping to use the same buckle, make sure the strap you purchase has the same shape and size holes as your current strap.

What is your wrist size?

Your wrist size is the circumference of your wrist where you wear your watch. Measuring this will tell you what length of watch strap you will need.

How to measure your wrist.

Measuring your wrist is a simple as wrapping a tape measure around your wrist and taking a note of the size. If you don't have a tape measure, you can achieve the same result by wrapping a piece of string around your wrist and then measuring this against a ruler.

What to remember.

• Always measure your wrist where you wear your watch, as this is a completely personal preference this is different for each person.
• Wrap the tape or string around your wrist as tight, or as loose as you would wear your watch to give the most accurate reading.

One last thing:

Important: A 170mm wrist size doesn't necessarily mean you need a 170mm strap. Remember to factor in the lug-to-lug distance and the overlap when the strap goes through the buckle. We'll cover strap length calculation below.

Time for some simple maths.

Calculating your fastened watch strap length:

(wrist size) – (lug-to-lug distance) = (done up strap length)

As an example, I will show my strap length for a Studio Underd0g using my wrist size:

175mm – 41mm = 134mm done up strap length.

A Good Rule to Remember

As a rule of thumb you want the total length of the strap to be around 40mm longer than your done up strap size. By doing this we are making sure the strap will fit us in one of the central holes. This differs for every strap depending on the shape, but I have found 40mm to be around the right size for most straps.

Finding your perfect strap.

Shopping for your new strap:

When shopping for a watch strap on watchobsession.co.uk you will see various options on each product page:

• Colour Options: clicking through these colours will take you to the product page of each individual colour.

• Width (Lug/Buckle): Usually written "20mm/18mm" where the first number is the lug width of the width, and the second is the buckle width.

• Length: Most often written "110mm/70mm", where the two numbers represent the lengths of the two ends of the watch strap. If you add these two lengths up you will get the total length of the strap.

• Buckle Option: This is where you can choose the buckle colour, or clasp colour of your new strap. This option can effect the price as clasps have an additional cost, if the colour you are after is not an option, they can more than likely be added separately at the same price.

Final Considerations

Strap Thickness.

The thickness of the strap can affect the length of the strap needed, thicker straps will need to be slightly longer to wrap around the wrist.

How tight you wear your watch.

This is another area that can affect your required strap length, as everyone is different, the best advice we can give is to make sure you measure our wrist size using a tape measure or string at the same tightness as you would wear your watch.

Watch strap style.

Watch straps come in various different styles, some like nylon straps, also known as one-piece straps, among other names, are actually designed to be longer and fold back on themselves to allow for greater adjustment. Some two piece straps do the same, in these cases its good to double check the strap sizing to be sure to get what you need.

Dive Straps.

If you are going to be diving with your new strap, make sure the strap will fit over your wetsuit by measuring your wrist size whilst wearing it, many dive watch straps, like the ISOfrane Rubber Dive Strap, have considerably more holes than usual to allow the strap to be worn comfortable with or without a wetsuit.