Atelier notes
How to measure a finger
Ten habits jewellers use before they cut a shank. Read these before you trust a number.
01
Measure at the end of the day
Fingers swell as you move. A morning size can feel tight by dinner. Sit in a warm room, at rest, and take the reading in the evening.
Skip the tape if you have just exercised, flown, eaten a salty meal, or come in from the cold. Wait until your hands feel ordinary.
02
Paper or string, done properly
Cut a strip of paper about 4 mm wide, or use non-stretch string. Wrap it around the base of the finger — not the knuckle — snug but not strangling.
Mark where the strip overlaps. Lay it flat against a millimetre ruler. That length is the inside circumference. Enter it in the Paper strip tool; we convert it to every size system.
Repeat three times. Use the middle value, not the average of a wild outlier.
03
Match a ring you already wear
This is the most accurate at-home method. Take a ring that already fits the same finger. After you line up a bank card on the screen, place the ring over the circle and step sizes until the inner edge sits flush.
Read the inside of the band, not the outside. Stone settings and thick shanks hide the true inner diameter.
04
Knuckle versus base
The ring has to pass the knuckle and then sit at the base. If the knuckle is much larger, size for the knuckle — a ring that will not go on is useless, even if the base is smaller.
A comfort-fit band (rounded inner profile) slides over a knuckle more easily than a flat court profile. Mention this to the jeweller if you live between two sizes.
05
Wide bands need a larger size
A 2–3 mm band feels true to the chart. From about 6 mm the same inner diameter sits tighter because more skin is in contact.
Rule of thumb: go up a half size for bands 6 mm and wider, a full half to a full size for extra-wide cigar bands. CIRCA shows this as a recommendation — it does not silently change your number.
06
Left, right, and the dominant hand
The dominant hand is often a quarter to a half size larger. Measure the finger that will actually wear the ring.
Thumb, index, and middle fingers are usually larger than the ring finger. Never reuse one number across the hand.
07
Heat, cold, water, and altitude
Cold shrinks fingers; heat and humidity swell them. Measure in the climate you live in, not a blasting air-conditioned shop if you can help it.
Pregnancy, medication, and long flights can move a size by half a step. If you are buying for a date months away, re-check close to the day.
08
US, UK, ISO, and Japan
US and Canada share one numeric scale. The UK uses letters. Europe mostly uses ISO 8653 — the inner circumference in millimetres. Japan uses a separate integer scale.
Always convert from millimetre diameter or circumference, not by guessing adjacent numbers. A UK N is not a US 7. The chart in CIRCA is ISO-aligned.
09
Snug, comfort, and stacking
A well-fitted ring turns with a slight effort and does not spin freely. It should not leave a deep indent or go white at the skin.
Stacked bands need a touch more room than a single slim ring. If you plan to wear two or three together, size the stack, not each band in isolation.
10
When to see a jeweller
Use CIRCA to get close. For a wedding band, an heirloom, or anything you cannot easily resize, confirm on a metal finger gauge or mandrel in a shop.
Some metals resize freely (yellow gold, platinum with care). Eternity bands, titanium, tungsten, and many patterned shanks do not. Get the size right the first time.
Ready to measure? Open the sizer or print a paper gauge.