Ring Size Guide

Four people can measure the same finger and produce four different sizes, each one reading correctly off the tool in front of them. A whole US size adds 0.81mm to a band’s inside diameter, and nothing enforces even that much. What ends up on the order also depends on the width of the band you are buying and the hour you were measured.

What a Ring Size Measures

Every sizing system measures the band’s inside diameter or inside circumference. A finger never enters the calculation. A band is a rigid circle and a finger in cross-section is closer to a flattened oval, so a ring touches skin at two points and bridges the gaps between them. That bridging is why one size can be comfortable on one hand and loose on another, even if they measure identically.

The US, Canada, and Mexico share a numeric scale in quarter steps. One whole size is worth 0.81mm of inside diameter, or 2.55mm of circumference. Half sizes are the working resolution. A bench jeweler building from a measurement works in quarters, and sizes below 3 or above 13 come in as specials.

Ring Size Conversion Chart

GOODSTONE rings are built to US sizes, with quarter sizes for anyone who falls between two.

European and ISO numbers are the inside circumference in millimeters. The right-hand column doubles as the European size and needs no conversion. The UK, Ireland, Australia, and New Zealand use letters in half steps. 

Published charts disagree by half a letter in places because the letter column is a rounding decision. The full international chart carries the half and quarter sizes, plus the letter and Japanese equivalents. 

To read the chart from a ring you already own, measure the inside edge of the band. Measuring across the outside adds the wall thickness twice, so a 1mm wall reads about two and a half sizes high.

Measuring Your Ring Size at Home

A measurement taken at home is worth having before a shop visit, since it tells you when a shop’s answer is off by a size. It is not enough to order from on its own.

String and paper strips read small, and a printable chart is accurate only when it prints at full scale. The check for each method is in How to Find Your Ring Size. A set of graduated steel rings, around 30, is what a shop reaches for, and the set costs less than a single resize. 

What Changes the Size You Need

A wide band needs a larger size than a narrow one because it traps skin underneath. Skin that would displace around a 2mm wire has nowhere to go under an 8mm slab, so the band binds at a size that would be correct for something thin. The width at which sizing guidance adds to the size ranges from about 4mm to 10mm, with adjustments from a quarter size up to a full one. That spread is wide enough that no rule replaces checking the specific band.

Standard fit, also sold as flat fit, has a flat inner wall like a length of pipe. Comfort fit domes that wall so it curves away from the finger at the edges. The two also read differently on a mandrel. A flat band is measured at its leading edge and a domed one at its centerline, so a comfort fit band in the same marked size arrives looser on the hand. How much looser is not settled, and advice on sizing down for it ranges from none to half a size. Ask to be sized on a comfort fit gauge.

The two adjustments do not stack. Width can move the size by up to a full size on a band over 4mm. That is more ground than the comfort fit reduction covers, so on a wide domed band the reduction disappears into it. Measure with a sizer in the width and profile you are buying, or buy where an exchange is available.

Where the knuckle is wider than the base of the finger, many jewelers measure both. A ring built to the base measurement has to be forced over the joint. Building to the knuckle leaves slack at the base, and a spring insert or beads inside the shank take up that slack. The gap generally has to reach about a size and a half before that work is worth doing.

Fingers move about a quarter to a half size across a single day, and roughly that much again between a cold morning and a humid afternoon. They are swollen on waking and settle through the morning. By evening, after use, they reach their largest size. Mid-afternoon is the closest thing to an average. Heat dilates the vessels near the skin and adds volume, as do salt, alcohol, a long flight, or hard exercise. Cold hands read small enough to throw off the measurement, so postpone it.

Measure three times on separate days at the same hour and use the middle figure.

Getting Measured in a Shop

Ring mandrels are not standardized between manufacturers, so a size 7 on one shop’s steel stick can read 7.5 on the next shop’s. Both are used daily by people who trust them. That is how a size taken at one counter and a ring built at another bench arrive wrong with nobody at fault. The fix takes one extra sentence. 

Ask for the inside diameter in millimeters at the size the jeweler measured, alongside the size itself. Any bench that owns a pair of calipers can produce that figure, and a measurement in millimeters survives a phone call in a way that 6.75 does not. 

Check the fit while the sizer is still on your hand. Take it off and put it back on. It should pass the knuckle under pressure and turn at the base without sliding back toward the first joint.

Ring Size Questions

What if I fall between two sizes?

Order the quarter size. Quarter steps are finer than the half sizes most stock bands come in, so an in-between measurement does not have to be rounded off. Where only half sizes are offered, and the number is a guess, take the larger of the two. A loose band can be tightened. One that will not pass the knuckle has to go back to the bench before it can be worn.

Should a wedding band be the same size as the engagement ring?

Not necessarily, because the two are worn stacked and behave like one wide band on the finger. A narrow engagement ring measured at a 6 and a 6mm anniversary band bought at 6 will not both fit comfortably. Size the pair together, on the finger, with both on at once.

Does the dominant hand measure differently?

The dominant hand frequently measures a quarter to a half size larger. Measure the specific finger on the hand the ring will be worn on, and say which hand it was when you give the number to a jeweler.