The complete ring measurement guide โ all methods explained, tools needed, circumference formula, inner diameter conversion, knuckle sizing, ring style adjustments, common mistakes, full UK chart AโZ+2 & free calculator
Every ring measurement method follows one of two routes: Route 1 measures the finger directly and gives circumference in mm. Route 2 measures an existing ring's inner diameter in mm and converts using ร ฯ (3.1416). Both routes end at the same UK ring size chart โ match your mm value to the Circ. (mm) or Diam. (mm) column.
Cut 4โ6mm wide strip, wrap at base, mark overlap, measure mm ร 3, average. ยฃ0 cost. ยฑ0.5mm accuracy.
Non-stretchy floss or cotton thread. Wrap once, mark, measure mm flat on ruler. No tools needed beyond ruler.
Flexible fabric sewing tape in mm. Wrap once and read circumference directly. Fastest single-step method.
Inner diameter in mm ร ฯ (3.1416) = circumference. Standard ruler gives ยฑ0.5mm โ free and reliable.
Inner diameter to ยฑ0.01mm. Under ยฃ10 from Amazon UK. Best for non-resizable metals (tungsten, ceramic, titanium).
Adjustable plastic loop reads UK letter size directly โ no conversion needed. Under ยฃ2 from Amazon UK.
Non-stretchy, free, 4โ6mm wide ร 10cm long. Best all-round finger measurement tool for ring sizing.
Thin, non-stretchy, found in every home. Use plain unwaxed floss โ waxed versions can slip and give a small reading.
Standard ruler with clear mm markings. Transparent rulers are easier to read on short measurement strips.
Under ยฃ10 on Amazon UK. ยฑ0.01mm accuracy for ring inner diameter. Essential for non-resizable ring metals.
Flexible, mm-marked tape. Wraps directly around the finger for a one-step circumference reading.
Under ยฃ2 from Amazon UK. Adjustable loop reads UK letter size directly on the tool โ zero conversion needed.
Elastic or ribbon โ stretches under tension, reads too small.
Wool or thick yarn โ compresses and gives an inaccurate circumference.
Wide sticky tape / plasters โ over 1cm wide, reads 1โ2mm too large.
Rigid builder's steel tape โ cannot wrap around a finger.
Cling film or kitchen foil โ too flexible, produces unreliable readings.
Paper strip / string / tape measurement โ use Formula 1 (match circumference in mm directly to chart).
Existing ring measured with ruler or calliper โ use Formula 2 (multiply inner diameter ร ฯ).
You know circumference but need diameter โ use Formula 3 (divide by ฯ).
Measurement is in inches โ use Formula 4 (multiply ร 25.4 first, then Formula 1).
Measure in the early evening (5โ9pm) at comfortable indoor temperature (18โ22ยฐC). Avoid measuring immediately after cold weather, a hot bath, exercise or a very salty meal โ all temporarily change finger circumference by up to 1mm.
Use standard printer paper or thin card. Cut cleanly to between 4 and 6mm wide. A strip over 1cm wide produces a reading 1โ2mm too large. This is the most common paper strip error for ring measurement.
Measure the exact finger and hand where the ring will be worn. The dominant hand is typically ยฝโ1 UK size larger than the non-dominant hand. Never substitute another finger or hand โ the result will not match.
Wrap the strip around the base of the finger โ snug but not tight. Mark precisely where the end first meets the rest of the strip with a fine-tip pen or sharp pencil. A thick or smudged mark adds up to 1mm error.
Lay flat on a mm ruler. Measure from the very start of the strip to the pen mark in millimetres (mm). Align with a clear mm division โ not the physical ruler end, which often has an offset gap before zero.
Three readings averaged reduces error from ยฑ1.5mm to under ยฑ0.5mm. Record all three values and calculate the average. Never rely on a single ring measurement for purchasing a ring.
Find your averaged mm in the Circ. (mm) column of the chart below. If your reading falls between two rows, always choose the larger UK size. A slightly large ring is adjusted easily; a tight ring restricts circulation.
Only use a ring that fits well and is worn on the specific finger and hand where the new ring will be worn. A ring from a different finger or the opposite hand can give a result up to one full UK size off.
Look at the inner band with a magnifying glass or phone camera. A UK letter (AโZ), US number (1โ13.5) or EU size (37โ72) stamped inside means the ring size is already known โ no measuring required. Match non-UK stamps to the chart below.
Lay the ring flat on a hard surface. Place a mm ruler across the centre. Measure from one inner edge to the directly opposite inner edge in mm. Never measure the outer diameter โ it includes band thickness and reads 2โ4mm too large.
Multiply inner diameter ร 3.1416 for circumference in mm. Enter into the calculator below for instant UK size conversion. Or match directly to the Diam. (mm) column in the chart below.
Use a digital calliper (under ยฃ10 from Amazon UK) for any ring in a non-resizable metal โ tungsten, ceramic, titanium or cobalt. These metals cannot be resized after purchase. A calliper gives ยฑ0.01mm accuracy, eliminating all measurement error before ordering. For standard gold, silver or platinum rings that can be resized, a free mm ruler is perfectly sufficient.
Every ring measurement must account for the knuckle โ the ring must pass over the knuckle to be worn and removed. If the knuckle is significantly wider than the finger base, sizing for the base alone will result in a ring that cannot be put on.
Use the paper strip method at the base of the finger and at the widest part of the knuckle. Record both readings in mm separately before deciding on a size.
If knuckle reads within 2mm of the base reading, size for the base. The ring will fit comfortably at rest and pass over the knuckle with slight resistance during wear and removal.
Average the base and knuckle mm readings. Example: 53.8mm + 57.6mm รท 2 = 55.7mm โ UK O or P. This gives a ring that passes the knuckle and fits acceptably at the base.
Size for the knuckle measurement and use a silicone ring adjuster insert at the base (under ยฃ3 on Amazon UK). This is the most comfortable long-term solution for significantly larger knuckles.
Your finger measurement gives a base size. The actual size you order must be adjusted depending on ring band width and style โ wider bands fit tighter and require a larger size than your measurement alone indicates.
Standard solitaires, thin bands and most everyday rings. No adjustment needed โ order the UK size that matches your mm reading directly from the chart.
Wide bands cover more of the tapered finger surface and fit tighter than a narrow ring at the same diameter. Order ยฝ UK size larger than your base measurement. Example: UK N โ order UK O.
Full eternity bands and very wide rings fit significantly tighter and are usually non-resizable. Order 1 full UK size up from your base measurement. Example: UK N โ order UK P.
Comfort-fit rings have a rounded inner profile that sits slightly looser. Most wearers find their standard size fits; others prefer ยฝ size up. If unsure, order ยฝ UK size up.
Fingers are at their smallest in the cold morning. This produces a reading up to 2mm too small โ equivalent to one full UK size. Always measure in the evening at room temperature.
A wide strip sits unevenly on the curved finger and reads 1โ2mm too large. Always cut paper or string to between 4 and 6mm wide for accurate ring measurement.
A single measurement can vary by ยฑ1.5mm due to tension and technique. Always measure three times with fresh strips and average the results before matching to the chart.
The outer diameter includes band thickness and gives a reading 2โ4mm too large. Always measure the inner diameter of a ring โ from inner edge to inner edge across the centre.
Elastic, wool, ribbon or stretchy thread compresses under wrapping tension and reads smaller than the actual circumference. Only use non-stretchy materials: paper, unwaxed floss, cotton thread.
The dominant and non-dominant hands differ by ยฝโ1 UK size. Always measure the exact finger and hand where the ring will be worn โ never substitute another finger as a proxy.
| UK Size | Circ. (mm) | Diam. (mm) | Circ. (cm) | Circ. (inches) | ๐บ๐ธ US Size | ๐ช๐บ EU Size | Best For |
|---|---|---|---|---|---|---|---|
| A | 37.8 mm | 11.9 mm | 3.78 cm | 1.488โณ | โ | 37 | Children / XS |
| B | 39.1 mm | 12.3 mm | 3.91 cm | 1.539โณ | 1 | 38 | Children / XS |
| C | 40.4 mm | 12.7 mm | 4.04 cm | 1.590โณ | 1.5 | 40 | XS Women |
| D | 41.7 mm | 13.1 mm | 4.17 cm | 1.642โณ | 2 | 41 | Small Women |
| E | 42.9 mm | 13.5 mm | 4.29 cm | 1.689โณ | 2.5 | 42 | Small Women |
| F | 44.2 mm | 13.9 mm | 4.42 cm | 1.740โณ | 3 | 43 | Small Women |
| G | 45.5 mm | 14.3 mm | 4.55 cm | 1.791โณ | 3.5 | 45 | Women |
| H | 46.8 mm | 14.7 mm | 4.68 cm | 1.843โณ | 4 | 46 | Women |
| I | 48.0 mm | 15.1 mm | 4.80 cm | 1.890โณ | 4.5 | 47 | Women |
| J | 48.7 mm | 15.5 mm | 4.87 cm | 1.917โณ | 4.75 | 48 | Women |
| K | 50.0 mm | 15.9 mm | 5.00 cm | 1.969โณ | 5 | 49 | Women |
| L | 51.2 mm | 16.3 mm | 5.12 cm | 2.016โณ | 5.5 | 50 | Women |
| M | 52.5 mm | 16.7 mm | 5.25 cm | 2.067โณ | 6 | 51 | Women |
| N โญ | 53.8 mm | 17.1 mm | 5.38 cm | 2.118โณ | 6.5 | 52 | Women's Avg โญ |
| O โญ | 55.1 mm | 17.5 mm | 5.51 cm | 2.169โณ | 7 | 54 | Women Popular |
| P โญ | 56.3 mm | 17.9 mm | 5.63 cm | 2.217โณ | 7.5 | 55 | Women Popular |
| Q | 57.6 mm | 18.2 mm | 5.76 cm | 2.268โณ | 8 | 57 | Slim Men |
| R | 58.9 mm | 18.6 mm | 5.89 cm | 2.319โณ | 8.5 | 58 | Lean Men |
| S | 60.2 mm | 19.1 mm | 6.02 cm | 2.370โณ | 9 | 60 | Avg Slim Men |
| T โญ | 61.4 mm | 19.56 mm | 6.14 cm | 2.417โณ | 9.5 | 61 | Men's Avg โญ |
| U โญ | 62.7 mm | 19.96 mm | 6.27 cm | 2.469โณ | 10 | 63 | Men Popular |
| V โญ | 64.0 mm | 20.37 mm | 6.40 cm | 2.520โณ | 10.5 | 64 | Men Popular |
| W | 65.3 mm | 20.78 mm | 6.53 cm | 2.571โณ | 11 | 65 | Athletic Men |
| X | 66.6 mm | 21.18 mm | 6.66 cm | 2.622โณ | 11.5 | 67 | Broad Men |
| Y | 67.8 mm | 21.59 mm | 6.78 cm | 2.669โณ | 12 | 68 | Large Build |
| Z | 68.5 mm | 21.79 mm | 6.85 cm | 2.697โณ | 12.5 | 69 | XL Build |
| Z+1 | 69.7 mm | 22.20 mm | 6.97 cm | 2.744โณ | 13 | 70 | XL Custom |
| Z+2 | 72.3 mm | 23.01 mm | 7.23 cm | 2.846โณ | 13.5 | 72 | Custom |