Ringsizely

US 5.5 to UK ring size

US ring size 5.5 is UK K½ — 16.10 mm inner diameter (50.6 mm circumference).

Your size is US 5.5 (UK K½, EU 51).

Fit confidence Exact table match

Fit confidence 70/100 · Medium Standard chart conversion; final fit still depends on band width and knuckle shape. Confirm with a printable or physical sizer before ordering an expensive ring.

US
5.5
UK
K½
EU / ISO
51
Japan
10
CH / IT / ES
11
Inner diameter, millimetres
16.10
Circ mm
50.6
Why this size?

Your input maps to US 5.5 — UK K½, EU 51, JP 10, Ø 16.10 mm.

Inner diameter is exact to about ±0.1 mm. String or on-screen methods add roughly ½–1 size of noise, so confirm with a second method before buying an expensive or non-resizable ring.

Open US 5.5 size guide

More options
Local only; no account.
Ring fit fix advisor

Choose the fit problem and get the safest next step before resizing, replacing or buying another ring.

Too tight or stuck Too loose or spinning Wide band or comfort-fit Non-resizable or brand ring

Nearby sizes

Nearby sizes
USUKInner diameter, millimetres
5J½15.70
6L½16.51

Frequently asked questions

Are US and UK ring sizes the same?

No — they use different scales, so the numbers do not match and must be converted. International equivalents are approximate; when possible, order by millimetre diameter.

I am between sizes — should I size up or down?

Measure again at a different time. If the result stays between sizes, compare band width, knuckle clearance, and the retailer's chart before choosing. A wider band can feel tighter than a narrow one at the same labelled size.

How should I confirm a converted ring size before ordering?

Measure the same finger or a ring that fits with a second method. For an expensive, wide, or non-resizable ring, check the retailer's chart and confirm with a physical sizer or jeweller.

Explore

Ring Size Conversions — All Systems & Sizes · Size 5.5 · See the full international ring size chart