The way an Apple Watch fits around your wrist may be adjustable, but the size of the case is crucial to get right before purchasing.
Starting with the Apple Watch Series 4, Apple moved to a new size standard for its smartwatches.
Apple Watch Series 6/5/4 and the all new Apple Watch SE now come in 40mm model and 44mm models.
For the first three generations of the Apple Watch - including the Series 3 (which is still on sale) - the sizes are 38mm and 42mm.
Not sure which Apple Watch size is for you? Let's go over how to measure your wrist and the key differences between the four models.
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Apple Watch sizes: How to measure your wrist
The fit of your watch is a fairly subjective thing, but it‚Äôs important to know just how big your wrist is before buying the Apple Watch or an additional band.
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So, how can you tell for sure? Well, get out the flexible tape measure and size up that wrist.
Hold the strip just below where your wrist bone sits and around where you would normally wear the band, wrap it around your wrist and line that up with the sizes of your Watch model.
Generally speaking, a small wrist is 5 - 6.5 inches and a large wrist is between 7 - 8.5 inches, but the good thing about many Apple Watch bands is that you can adjust with velcro or within the perforations of sports straps to find a very specific fit.
Just don't go too tight or too loose ‚Äď not only can it become uncomfortable, but it also affects the accuracy of the Apple Watch's heart rate monitor.
Apple Watch sizes: 38mm v 42mm & 40mm v 44mm
The newer Apple Watch Series 4 - Series 6 models come in 40mm and the 44mm - though you can still buy the older models (Series 3 or lower) with the 38mm and 42mm casing.
These measurements denote the size of the bezel, though the straps do always play a role in the specific fit of the smartwatch on your wrist. Apple also takes its Watch measurement vertically, as opposed to most other brands, which do so horizontally.
So, for the 40mm model, expect a width of 34mm, depth of 10.7mm and a case weight of around 30g. For the bigger 44m model, you'll have to deal with a width of 38mm, the same 10.7mm depth and a 36g case weight.
For the 38mm model, the width is 33.3mm, while the 44mm sibling has a width of 35.9mm. Again, like with the Series 4, there's no disparity in the depth of each device, with both coming in at 10.5mm.
These sizes are important for establishing which face will be best suited to your wrist, so it doesn't hurt to cut out a paper equivalent to compare on your wrist ‚Äď or, you know, just go to an Apple store and try on all four sizes.
The importance of picking the right band
What actually affects the comfort more, of course, is the material and tightness of the band.
Apple itself has a full guide to the specifics of each of its own band type (Modern Buckle, Sport, Milanese Loop, Classic Buckle and Link Bracelet), some of which you'll have to choose a size for when buying, and some (like the Sport bands) which come with both a S/M and M/L strap for you to pick from.
Remember, too, that all bands that worked with Series 1-3 will correspond with the bigger/smaller size of the Series 4 or Series 5. So, a 38mm Series 2 band will fit the 40mm Series 5.
There's also a full crop of third-party Apple Watch bands that you can explore. They're almost always cheaper, and many can pass as the same style as the Apple-own variants.