Ring Size Chart: find your size by measuring on screen

Between markers–

In inches–

Tape fraction–

Pixels–

Ruler length–

Hold an object against the screen inside the box, drag the box to move it, drag the dot to resize.

240 × 120 px

Drag until the outline matches your card's width exactly

Any standard bank, credit, debit, or ID card works: the ISO/IEC 7810 ID-1 format is exactly 85.60 mm wide everywhere in the world. Hold the card flat against the screen, match the width, then apply.

True actual size after calibration Inch fractions to 1/16, like a tape measure Corner ruler & measure box Free, private, works offline

Diameter is the truth

Measure a ring you own, read the size off the chart

Every ring sizing system is a label for the same physical fact: the ring's inside measurement. Calibrate this page once against a bank card, place a ring that already fits flat against the screen, and size the measure box, on by default below the ruler, until it just touches the inner edges; the readout gives the inside diameter in millimetres, and the chart converts it to a size. Measure across the widest point of the opening, keep your eye straight-on, and prefer a ring worn on the same finger you are buying for.

The chart

US ring sizes with diameter, circumference, and ISO

Computed from the standard US sizing relation, inside diameter = 11.63 mm + 0.8128 mm per size, with circumference = π × diameter. ISO 8653 designates rings by inner circumference in millimetres, shown rounded. UK letter conversions vary by up to half a letter between published charts, so for international orders give the seller the millimetre measurement itself.
US & Canada size	Inside diameter	Inside circumference	ISO size
3	14.07 mm	44.2 mm	44
3.5	14.47 mm	45.5 mm	45
4	14.88 mm	46.8 mm	47
4.5	15.29 mm	48.0 mm	48
5	15.69 mm	49.3 mm	49
5.5	16.10 mm	50.6 mm	51
6	16.51 mm	51.9 mm	52
6.5	16.91 mm	53.1 mm	53
7	17.32 mm	54.4 mm	54
7.5	17.73 mm	55.7 mm	56
8	18.13 mm	57.0 mm	57
8.5	18.54 mm	58.2 mm	58
9	18.95 mm	59.5 mm	60
9.5	19.35 mm	60.8 mm	61
10	19.76 mm	62.1 mm	62
10.5	20.16 mm	63.3 mm	63
11	20.57 mm	64.6 mm	65
11.5	20.98 mm	65.9 mm	66
12	21.38 mm	67.2 mm	67
12.5	21.79 mm	68.5 mm	68
13	22.20 mm	69.7 mm	70

Fit, honestly

What a chart cannot decide for you

Between sizes

Round up, usually

If the measurement lands between sizes, the common jeweller guidance is to take the larger one: a slightly loose ring goes on and comes off; a slightly tight one does neither. Half sizes exist precisely for this gap.

Wide bands

Width changes fit

Bands much wider than about 6 mm wear tighter than thin ones on the same finger, so jewellers commonly suggest considering the next half size up for wide styles. The chart gives the geometry; the style adjusts it.

Fingers vary

Measure at the right moment

Finger size shifts with temperature and time of day, typically smallest in cold mornings. Measure a comfortable existing ring rather than a cold finger, and for an expensive purchase, confirm with a jeweller's sizer; this chart is a guide, not a guarantee.

FAQ

Ring size questions, answered

How do I measure my ring size without a ring sizer?

Use a ring that already fits: calibrate this page against a bank card, hold the ring flat to the screen, and size the measure box to its inner edges for the inside diameter in millimetres, then read the size off the chart. Measuring an existing ring beats measuring a finger, which changes with temperature.

What diameter is a US size 7 ring?

About 17.32 mm inside diameter, which is roughly 54.4 mm of inner circumference, ISO size 54. Each whole US size step adds 0.8128 mm of diameter, so size 8 is about 18.13 mm and size 6 about 16.51 mm.

What if I am between ring sizes?

Take the larger size in most cases, especially for wider bands, which wear tighter. A ring must pass the knuckle comfortably; half sizes exist exactly for this situation, and a jeweller can fine-tune fit afterwards.

How do US sizes convert to UK letters?

Approximately, and that is the honest answer: published UK conversion charts disagree with each other by up to half a letter. The reliable route for any international order is the millimetre measurement itself, inside diameter or circumference, which every sizing system ultimately encodes.