A custom ring is made for one finger only — which is exactly why sizing deserves five careful minutes before you order. Most online custom jewelers, us included, will resize or remake if needed, but getting it right the first time saves weeks. Here are the four methods that actually work at home, ranked by reliability, plus the professional tricks that prevent the most common mistakes.
Method 1: Measure a ring that already fits (most reliable)
Take a ring that fits the intended finger perfectly and measure its inside diameter in millimeters with a ruler or caliper — straight across the center. Match that diameter to a conversion chart: 16.5mm is a US 6, 17.3mm a US 7, 18.1mm a US 8. If you are secretly sizing a partner, borrow a ring from the correct finger and trace its inside circle on paper; a jeweler can size a tracing with surprising accuracy.
Method 2: The paper or string method
Wrap a thin strip of paper around the base of the finger, mark where it overlaps, and measure the length in millimeters — that circumference converts directly to a size (52mm ≈ US 6, 54.4mm ≈ US 7, 57mm ≈ US 8). Measure three times at different hours: fingers swell in heat, shrink in cold and are largest at the end of the day. Use paper, not stretchy string, and pull it snug — not tight — over the knuckle.
Method 3: A printable ring sizer
Many jewelers publish printable sizing strips with a marked slot. Printed at exactly 100% scale (check the printed ruler against a real one), these are measurably better than string because they behave like a real band sliding over the knuckle.
Method 4: Order an inexpensive plastic ring sizer
For a few dollars, a reusable plastic sizer gives near-jeweler accuracy at home. If you are ordering a significant custom piece, this small step is the best insurance you can buy — and we are happy to guide you through it during your consultation.
◆The three mistakes that cause most sizing failures
Sizing only once instead of three times; forgetting that wide bands (6mm+) need a quarter to half size up; and measuring a different finger than the one the ring is for. Left and right hands often differ by half a size.
US sizes and inside diameter, at a glance
- US 5 — 15.7mm diameter, 49.3mm circumference
- US 6 — 16.5mm diameter, 51.9mm circumference
- US 7 — 17.3mm diameter, 54.4mm circumference
- US 8 — 18.1mm diameter, 57.0mm circumference
- US 9 — 19.0mm diameter, 59.5mm circumference
- US 10 — 19.8mm diameter, 62.1mm circumference
What if the ring still doesn’t fit?
Reputable custom jewelers plan for this. Small adjustments of half to one full size are routine for solid gold and platinum bands; we handle resizing and will always tell you upfront if a design (like full eternity bands set with stones all around) resizes poorly — before you order, not after. When in doubt, tell your jeweler your measurement and let them recommend the size; it is what we do every day.
Sized right, made once
When you order a custom ring from us, sizing is part of the free consultation: send us your measurement by any method above, and we will confirm the size, the band width allowance and the fit before a single gram of gold is cast.
Written by
Lisa M.
Lead Jewelry Designer · 25+ years at the bench. Lisa has designed custom pieces for clients in 60+ countries, from single-name necklaces to heirloom redesigns.
