Ring Size Guide: How to Measure, Convert & Get It Right
A practical reference for measuring ring size at home, sizing a partner's finger for a surprise proposal, converting between US, UK, and EU systems, and avoiding the most common sizing mistakes.
Updated · 8 min read
Four ways to measure, ranked by accuracy
1. Plastic sizer kit (most accurate)
Order a free sizer kit from any major jeweler — they ship in a few days. The kit includes a strip of plastic loops at every half-size; you slide one onto your finger and pick the one that goes over the knuckle with light resistance and rests comfortably. Order the kit at least a week before you need to buy a ring.
2. Existing ring + mm measurement
Take a ring she wears on the intended finger and measure the inside diameter in millimeters using a ruler or caliper. Cross-reference the mm value against the conversion table below. This is the most reliable method for surprise sizing because it requires only one item from her drawer.
3. In-person jeweler measurement
The standard reference. Any jewelry store will size your finger free of charge with a metal ring-sizer tool. Use this when you have access — it's the same physical instrument the jeweler will use when sizing the final ring.
4. Paper-strip method (last resort)
Wrap a strip of paper around the finger, mark where it overlaps, and measure the length. Divide by π (3.14159) to get the diameter, then convert to ring size. Paper stretches and bends — this method consistently reads one full size larger than the actual measurement. Use it only if no other option exists.