Measure the inside diameter of a ring that fits that finger.
Step 1: Place the ring on a flat surface.
Step 2: Measure straight across the inside of the ring (mm).
Step 3: Use the calculator below to get your suggested UK letter size.
Tip: If your ring is slightly oval, rotate it and measure again — use the average.
Ring inner diameter (mm) → Suggested UK Size
Enter the inner diameter of your ring in mm. We’ll suggest the closest UK letter size.
mm
Suggested UK size: —
Tip: measure 2–3 times and use the average.
DIAMETER (MM)
UK SIZE
≈ 15.7
K
≈ 16.5
M
≈ 17.3
O
≈ 18.1
Q
≈ 19.0
S
≈ 19.8
U
≈ 20.6
W
≈ 21.4
Y
≈ 22.2
Z
If you’re between sizes, choose the larger size for comfort (especially with wider bands).