Radiant-Cut Black Diamond Cathedral Engagement Ring

Measure your finger

1. Wrap a piece of string, or a thin strip of paper, around the base of the finger. Snug, not tight.

   

2. Mark the point where the end overlaps.

   

3. Lay it flat against a ruler and read the length. That is the inside circumference. The chart below is in millimeters, so 5.4 cm on a metric ruler means 54 mm.

   

Or measure a ring that already fits

Place the ring on a ruler and measure straight across the inside, edge to edge. Match that to the inside diameter column. Use a ring worn on the same finger — sizes differ from hand to hand.

US ring sizes

Before you decide

• Measure late in the day. Fingers are smallest in the morning and in the cold, and a reading taken then will come out a size small.
• Check the knuckle. The ring has to pass over it. If the knuckle is much larger than the base of the finger, size to clear the knuckle.
• Wide bands fit closer. For a band wider than about 6 mm, allow a quarter to half size up.
• Between two sizes? Take the larger one. A slightly loose ring can be adjusted; one that will not pass the knuckle cannot be worn.

Full ring size chart and how to measure at home