Convert ring sizes between US, UK, EU, inside diameter, circumference, millimeters, and inches. Use this converter to compare international ring sizes and estimate ring size from finger or ring measurements.
Diameter to circumference:
circumference = diameter × π
Circumference to diameter:
diameter = circumference ÷ π
Millimeters to inches:
inches = mm ÷ 25.4
Inches to millimeters:
mm = inches × 25.4
Ring size conversions are useful for engagement rings, wedding bands, fashion rings, international jewelry shopping, resizing, gift buying, comparing US, UK, and EU sizes, and converting diameter or circumference measurements.
Use this converter as an estimate, then confirm sizing with a jeweler or official ring size chart.
Your result shows the entered ring size or ring measurement converted into the selected size system. The converter also displays approximate matching values for US size, UK reference, EU size, inside diameter, and inside circumference.
Ring sizing is not always exact. Fit can vary based on band width, knuckle size, finger swelling, temperature, ring shape, material, and how snug or loose you prefer the ring.
Measure the inside diameter of the ring, then convert that diameter to a US, UK, or EU ring size estimate.
EU ring size is often close to the inside circumference of the ring in millimeters.
US ring size 7 is commonly around EU size 54, but charts can vary slightly.
No. Ring size conversions are estimates because different charts, band widths, and fit preferences can vary.
Often, yes. Wide bands can feel tighter than thin bands, so some people choose a slightly larger size.