Convert US (us) to MM (mm) instantly. US ring size to circumference in mm.
| Unit | Name | Value |
|---|---|---|
| uk | UK / Australia | — |
| eu | EU / Germany | — |
| mm | Circumference (mm) | — |
💡 Tip: Measure your finger circumference in mm — EU size = circumference in mm exactly. Divide by π (3.14159) to get diameter.
All standard sizes — with finger circumference and diameter for reference
| US / Canada | Circumference (mm) | Measurement |
|---|---|---|
| 3 | 44.2 | 44.2 mm circ / 14.1 mm dia |
| 3.5 | 45.5 | 45.5 mm circ / 14.5 mm dia |
| 4 | 46.8 | 46.8 mm circ / 14.9 mm dia |
| 4.5 | 48.0 | 48.0 mm circ / 15.3 mm dia |
| 5 | 49.3 | 49.3 mm circ / 15.7 mm dia |
| 5.5 | 50.6 | 50.6 mm circ / 16.1 mm dia |
| 6 | 51.9 | 51.9 mm circ / 16.5 mm dia |
| 6.5 | 53.1 | 53.1 mm circ / 16.9 mm dia |
| 7 | 54.4 | 54.4 mm circ / 17.3 mm dia |
| 7.5 | 55.7 | 55.7 mm circ / 17.7 mm dia |
| 8 | 57.0 | 57.0 mm circ / 18.1 mm dia |
| 8.5 | 58.3 | 58.3 mm circ / 18.6 mm dia |
| 9 | 59.5 | 59.5 mm circ / 18.9 mm dia |
| 9.5 | 60.8 | 60.8 mm circ / 19.4 mm dia |
| 10 | 62.1 | 62.1 mm circ / 19.8 mm dia |
| 10.5 | 63.4 | 63.4 mm circ / 20.2 mm dia |
| 11 | 64.6 | 64.6 mm circ / 20.6 mm dia |
| 12 | 67.2 | 67.2 mm circ / 21.4 mm dia |
| 13 | 69.7 | 69.7 mm circ / 22.2 mm dia |
Each US half size ≈ +1.3 mm circumference.
mm circ ÷ π (3.14159) = diameter in mm. US 7 = 54.4 mm circ = 17.3 mm dia.
Wrap paper around finger, mark overlap, measure = mm circumference = EU size.
Converts US / Canada ring size to Circumference (mm) when purchasing from international online jewellers.
Converts customer-provided ring sizes to the sizing system used by their tools and ring blanks.
Converts a partner's known ring size to the size system used by an international jeweller.
Compares ring sizes from different measurement methods before placing a custom order.
Lists ring sizes in multiple systems on product pages for international customers.
Finds the correct local ring size equivalent when shopping for jewellery abroad.
US and Canadian ring sizes use a numerical scale (0–13+) where each half size corresponds to a finger circumference increment of about 1.3 mm. The system has no standardized international anchor — US size 7 ≈ 54.4 mm circumference, widely used as a reference for a 'medium' adult ring.
US ring sizing is the most common reference in online jewellery sales globally. Most international jewellers list US sizes alongside their local system. The average US women's ring size is 6–7; men's 9–10.
Interesting fact: Ring sizing developed from mandrel-based measurement — jewellers used tapered metal cones marked with arbitrary numbers. Different countries independently chose different numbering anchors, creating the incompatible systems that persist today.
Finger circumference in millimeters (mm) is the most universal and accurate ring size measurement. Measure by wrapping a strip of paper or string around the base of the finger, marking the overlap point, then measuring that length against a ruler.
The mm circumference is the physical anchor for all ring size systems: EU size = circumference in mm; US and UK sizes are derived from it via lookup tables. A 54 mm circumference corresponds to US 7, UK N, EU 54 — the most common 'average' adult size.
Interesting fact: The best time to measure ring size is at the end of the day when fingers are at their largest (they can vary by 0.5–1 mm throughout the day due to temperature and fluid retention). Measuring on a warm day gives the most inclusive fit.
Ring sizes are not internationally standardized. US/Canada use a numerical scale (0–13); UK/Australia use letters (A–Z+); EU/Germany use circumference in mm (the most physically direct system). The universal anchor: US 7 = UK N = EU 54 = 54.4 mm circumference = 17.3 mm diameter.
For the most accurate measurement, wrap a strip of paper around the base of your finger, mark the overlap, and measure in mm — that IS your EU size. Always measure at the end of the day.