Apple Watch - Size and compatibility

Finding Your Size

Apple Watch reading the 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.

Band Compatibility

Apple’s band system is designed to be stable across generations. That’s why an older 38mm band still fits a new 41mm case, and why a 44mm band 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)

Your watch’s name may change when you upgrade — the connector family doesn’t.