Finding Your Size
No guessing, no charts — just read the case size in millimeters on the back.
Step 1 — Confirm the mm size
Gently wipe the case back and look for mm. Examples: 41mm, 45mm, 49mm.
Step 2 — Pick your size
Small • 38/40/41 mm
Large • 42/44/45/49 mm
Pick the matching variant on the product page for a perfect click-in fit.
Tip: In a pinch, the Watch app → About → Model also confirms your case size.
Strap Compatibility
Apple’s strap system is designed to be stable across generations. That’s why an older 38mm strap still fits a new 41mm case, and why a 44mm strap locks perfectly into a 45mm or 49mm Ultra. Know your size family once; buy with confidence forever.
Works with:
•Small Family (38/40/41 mm)
→ Series 1–9 (small), SE
•Large Family (42/44/45/49 mm)
→ Series 1–9 (large), SE (large), Ultra & Ultra 2 (49mm)
•Small Family (38/40/41 mm)
→ Series 1–9 (small), SE
•Large Family (42/44/45/49 mm)
→ Series 1–9 (large), SE (large), Ultra & Ultra 2 (49mm)
Your watch’s name may change when you upgrade — the connector family doesn’t.