How big should your watch be? It’s not as simple as it sounds. You may know your Panerai from your Piaget, but understanding how a watch will sit on your wrist is about a lot more than its case measurements. Here are our expert tips for making sure you buy the watch that really suits your wrist.

You don’t shop for shoes, or a shirt, without knowing your size, but do you know your wrist measurement? Wrap a tape measure around your arm and check – most men’s wrists will be between 16cm and 23cm (6 to 9in). The numbers don’t tell the whole story, however.

A single figure is the industry standard for expressing a watch’s size: the diameter of the case, not including the crown or lugs. It’s useful to an extent, but you need to think about the watch as a whole. The human brain is not particularly good at translating a one-dimensional measurement into a two- or three-dimensional object. If you start with a 38mm round watch, every 2mm you add to the width of the case roughly equates to a 10 per cent increase in the area it takes up on your wrist. A 45mm watch is nearly one and a half times as big as a 38mm one.

There is a reason why we always list a watch’s height, or thickness, on MR PORTER. It’s a major factor in how it fits. There may only be a millimetre’s difference in their diameter, but this Piaget Altiplano is half the thickness of this Bremont watch. Thickness is important in assessing when you’ll wear the watch, too. If it’s going to snag on your shirt cuff, maybe opt for something a bit thinner.

Watch nerds talk about how a watch wears, often saying things such as, “It’s 40mm, but it wears bigger.” What are they on about? It’s simple. The proportions of a watch change your perception of its size. Watches with thin or no bezels, such as an IWC Schaffhausen Portugieser, have a much larger dial relative to the overall size of the watch. This makes it feel expansive and legible and contributes to an overall feeling of size.

So many factors can change whether a watch feels big or small beyond its absolute dimensions – the size of a watch’s lugs, the way the strap falls away from the case, the size of the crown or the raised height of the sapphire crystal. Even the style of strap is a factor. If you have narrow wrists, swapping a steel bracelet for a rubber or Nato strap can bring a watch into your range that wasn’t there before.

36mm and below

As a general rule, watches have been getting bigger since their introduction about a century ago. Today, the entry level size for a men’s watch is 36mm. Not all brands offer something at this level, but take a look at the NOMOS Glashütte Club Campus for an example. If you have small wrists, something between 36mm and 40mm is going to be your target. Square and rectangular watches also figure in this bracket. Their dimensions mean they will wear a little larger in reality. But it’s not just about your measurements. A smaller watch looks great on men with medium-sized wrists. It’s all about having the confidence to try it.

37mm to 41mm

This is the sweet spot for most men’s wrists. Over the past five years, more watch brands have reintroduced models at this size (having previously focused on larger timepieces) and we’re all better off for it. In this size bracket, you’ll find slender dress watches and sports models alike. The only thing you’re unlikely to see much of are the more complicated watches because the movements demand more space inside. It’s also worth mentioning that between 36mm and 40mm is the ideal size for women looking to wear men’s watches.

42mm to 44mm

Beyond a 42mm case diameter, we’re edging into oversize territory, a trend kick-started by IWC and Panerai in the mid-1990s, whose respective Portugieser and Luminor were loud and proud torchbearers for Swiss watchmaking’s revival. The Portugieser was originally based on a 1930s pocket-watch movement and the Luminor was purpose-built for a military frogmen in the 1950s, who needed robust and legible watches. If you’re looking for a chronograph, diving watch or pilot’s watch, or if you have a wrist circumference over 20cm, 42mm to 44mm is definitely the bracket you want to shop within. It’s well served by nearly every watchmaker.

45mm and above

Unless you’re a world champion arm wrestler, the lugs of your watch are guaranteed to hang over your wrist at this size. Like capacious shoulder pads on a slim double-breasted jacket, it’s a look only a select few will carry off. Believe it or not, IWC’s Big Pilot started life at 55mm, strapped to the thighs of Luftwaffe bomber navigators during WWII, so it’s almost the subtle choice, in a way. Some oversized watches are all about making an impression, however – like this 45mm Ulysse Nardin Blast Automatic Tourbillon.