Apple Watch straps are sold by case size, and your case size is engraved in millimetres on the back of the watch. That sounds simple until you meet the number 42. Apple has made two different 42mm watches, years apart, and they do not take the same straps.
Below: Apple's two strap groups, how to find your size, and the right option on each of our seven straps, named exactly as the product page names it.
Read the case size on the back of your Apple Watch, then choose the strap option that names it. Apple splits sizes into two strap groups: 38, 40 and 41mm plus the 42mm of Series 10 and later take the smaller straps; 44, 45, 46 and 49mm plus the 42mm of Series 3 and earlier take the larger ones. The two 42mm watches do not share straps.
- Smaller strap group: 38, 40, 41mm and the 42mm of Series 10 and later.
- Larger strap group: 44, 45, 46mm and the 42mm of Series 3 and earlier. Apple Watch Ultra (49mm) also takes 44, 45 and 46mm straps.
- All seven of our straps offer a 49mm (Ultra) option. Only Bergamo lists 38mm.
- If our page does not name your exact watch, write to us before you order.
How do I find my Apple Watch case size?
Two ways, each under a minute.
- Turn the watch over. Apple's advice is to check the engraving on the back of your Apple Watch. The case size is part of it: 41mm, 45mm, 46mm and so on.
- Use the Watch app on your iPhone. Open the My Watch tab, tap General, then About, and find Model Number. Tap it once and it shows a five-digit number beginning with "A". Apple's "Identify your Apple Watch" page lists every model number with its series and case size.
The number is the height of the case, not the screen. Apple gives the 42mm Series 10 as 42mm high and 36mm wide, and the 46mm as 46mm high and 39mm wide.
For 42mm you need the series too, for the reason below. Every one of our strap pages, from Cremona to Bergamo, asks for this choice first.
Which Apple Watch sizes share the same straps?
Apple Watch straps fall into two groups by case size. A strap made for one model fits another as long as both sit in the same group. From Apple's model list and strap compatibility page:
| Apple Watch | Case sizes | Strap group |
|---|---|---|
| Apple Watch (1st generation), Series 1, 2 and 3 | 38mm or 42mm | 38mm: smaller. 42mm: larger |
| Series 4, 5, 6, SE, SE 2 and SE 3 | 40mm or 44mm | 40mm: smaller. 44mm: larger |
| Series 7, 8 and 9 | 41mm or 45mm | 41mm: smaller. 45mm: larger |
| Series 10, 11 and 12 | 42mm or 46mm | 42mm: smaller. 46mm: larger |
| Ultra, Ultra 2, Ultra 3 and Ultra 4 | 49mm | Larger, with its own 49mm straps |
Apple's own store now sells its smaller straps as 42mm and lists them for 38, 40, 41 and 42mm cases. It sells the larger ones as 46mm and lists them for 44, 45, 46 and 49mm cases. So a strap you bought for a 45mm Series 7 will fit a 46mm Series 11. Of our straps, only Bergamo names every size from 38mm to 49mm.
Why are there two different 42mm Apple Watches?
Because Apple used the number twice, at opposite ends of the range.
- The original 42mm belongs to Apple Watch (1st generation) and Series 1, 2 and 3. It was the larger size, next to 38mm, and takes the larger straps. Apple's strap page still groups 42mm with 44 and 45mm, and that line refers to this older watch.
- The newer 42mm arrived with Series 10 in 2024 and continues on Series 11 and 12. It is the smaller size, next to 46mm, and takes the smaller straps, with 38, 40 and 41mm.
A strap made for one 42mm will not suit the other. Our Cremona and Bolzano pages, and Bergamo, label the newer size "42mm (Series 10 and later)". Where a 42mm sits next to 40 and 41mm, it is the newer one; where it is marked "Series 1–3", it is the older one.
What strap size fits Apple Watch Ultra?
Every Apple Watch Ultra, from the first to Ultra 4, has a 49mm case. Apple says the Ultra also takes 44, 45 and 46mm straps, but only for casual, everyday wear.
If you own an Ultra, choose the option on our page that says "49mm (Ultra)". All seven of our straps have one. Livorno and Monza list it for Ultra and Ultra 2, and Terni offers titanium-tone hardware, which its page says disappears into a natural Ultra case.
Which option should I choose on each of our straps?
Each strap page has a "Select your Apple Watch" menu. The second column copies its options exactly. The last three columns show which one to pick for the sizes that cause most questions.
| Strap | Options on the page | 42mm, Series 10 or later | 46mm, Series 10 or later | 42mm, Series 3 or earlier |
|---|---|---|---|---|
 Cremona
|
40 / 41mm · 42mm (Series 10 and later) · 44 / 45 / 46mm · 49mm (Ultra) | 42mm (Series 10 and later) | 44 / 45 / 46mm | 44 / 45 / 46mm |
 Bergamo
|
38 / 40 / 41mm · 42mm (Series 10 and later) · 44 / 45 / 46mm · 42mm Series 1–3 · 49mm (Ultra) | 42mm (Series 10 and later) | 44 / 45 / 46mm · 42mm Series 1–3 | 44 / 45 / 46mm · 42mm Series 1–3 |
 Bolzano
|
42mm (Series 10 and later) · 44 / 45mm · 46mm (Series 10 and later) · 49mm (Ultra) | 42mm (Series 10 and later) | 46mm (Series 10 and later) | 44 / 45mm |
 Monza
|
40 / 41 / 42mm · 44 / 45 / 46mm · 49mm (Ultra) | 40 / 41 / 42mm | 44 / 45 / 46mm | 44 / 45 / 46mm |
 Livorno
|
40 / 41 / 42mm · 44 / 45 / 46mm · 49mm (Ultra) | 40 / 41 / 42mm | 44 / 45 / 46mm | 44 / 45 / 46mm |
 Terni
|
44 / 45 / 46mm · 42mm Series 1–3 · 49mm (Ultra) | Does not fit | 44 / 45 / 46mm · 42mm Series 1–3 | 44 / 45 / 46mm · 42mm Series 1–3 |
 Trieste
|
40 / 41 / 42mm · 44 / 45 / 46mm · 49mm (Ultra) | 40 / 41 / 42mm | 44 / 45 / 46mm | 44 / 45 / 46mm |
The notes behind the table:
- Terni. It comes in the larger fitting only, plus Ultra. It fits 44, 45 and 46mm, the 42mm of Series 3 and earlier, and the 49mm Ultra. It does not fit the 42mm of Series 10 and later.
- Livorno, Monza and Trieste. Their "40 / 41 / 42mm" option is the smaller fitting, so it is the one for a 42mm of Series 10 and later. A 42mm of Series 3 or earlier takes the "44 / 45 / 46mm" option.
- Every strap. Apple's own rule holds across our range: the smaller fitting serves 38, 40, 41mm and the newer 42mm; the larger serves 44, 45, 46mm, the older 42mm and, with its own option, the Ultra.
Bolzano offers no 38, 40 or 41mm option. For materials and how each strap ages, see how to choose an Apple Watch strap.
Does strap size tell you if it fits your wrist?
No. Case size tells you whether the strap fits the watch, not your wrist. Three of our pages give a figure:
- Bergamo fits wrists from 130mm to 210mm. Seventeen pairs of magnets let it close wherever your wrist ends, not at a fixed hole.
- Cremona is 125mm + 75mm long, 24mm wide and 4mm thick.
- Bolzano is 125mm + 80mm long and 3mm thick.
For the others, measure a strap you already own and like. If you are unsure, Bergamo is the forgiving choice: no holes, so no "between two notches".
What should I check before I order a strap?
- Size: from the back of the watch, or the model number in the Watch app.
- Series, if your watch is 42mm: Series 3 or earlier takes the larger straps; Series 10 or later, the smaller ones.
- The exact option: pick the one that names your size. Do not round up or down.
- Anything unclear: write to us first. One message saves a return.
- Hardware: six of our seven straps offer a choice of buckle or hardware colour, so match it to your watch.
All seven pages describe a tool-free fit: the connectors slide straight into the watch case. Torn between Monza and a leather strap? Our comparison of leather, Alcantara and vegan leather explains the difference.
Browse all our Apple Watch straps, or read why our Cremona strap is named after the city of violins. Choosing a phone case too? Which case fits my iPhone? uses the same model-number method.
Frequently asked questions
Will a 44mm strap fit a 45mm or 46mm Apple Watch?
Yes. Apple says straps for 44, 45 and 46mm cases are compatible with each other.
Will a 41mm strap fit the 42mm Apple Watch Series 10 or 11?
They are in the same group: Apple lists its current 42mm straps for 38, 40, 41 and 42mm cases. On our pages, choose the option that names your 42mm watch, and ask us if none does.
Will my old 42mm strap fit a new 42mm Apple Watch?
No. The 42mm of Series 3 and earlier takes the larger straps; the 42mm of Series 10 and later takes the smaller ones.
Can I wear a 45mm strap on Apple Watch Ultra?
Yes, for casual, everyday wear, Apple says. For a strap made for the Ultra, choose our 49mm (Ultra) option.
Which of your straps fits a 38mm Apple Watch?
Only Bergamo lists 38mm, in its "38 / 40 / 41mm" option.
Written by the Capini Firenze team. Every size above was checked against Apple's pages and ours; we update it when Apple adds a size.
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