Ring Sizer Tool: Find Your Ring Size in mm (Free Online + Printable)
Use this free online ring sizer to measure ring size at home in under two minutes. Match a ring you already own on screen, enter a string measurement, or print an actual-size ring sizer. Results show your US, UK and EU ring size plus the exact inside diameter and circumference in millimetres.
Quick answer: how to find your ring size at home
- Have a ring that fits? Calibrate your screen with a credit card, place the ring on the circle below and adjust until the blue line sits just inside the ring. Read your size.
- No ring? Wrap a strip of paper or string around the base of your finger, mark where it overlaps, measure the length in mm and enter it in the ring size calculator.
- Want it on paper? Print the actual-size ring sizer at 100% scale and check the 50 mm test line with a ruler.
US size 7 = 17.3 mm inside diameter = 54.4 mm circumference. Each half US size adds about 0.4 mm to the diameter.
Online ring sizer tool: measure a ring on your screen
Screens differ in size, so this ring sizer tool online starts with a one-time calibration. Any standard bank card, ID card or loyalty card works, because they are all exactly 85.6 mm wide.
1 Calibrate with a card
Hold a card flat against the screen over the box. Move the slider until the box is exactly as wide as the card.
Not calibrated yet: using a typical screen setting.
2 Place a ring that fits
Lay the ring on the circle. Adjust until the blue line sits just inside the ring’s inner edge, touching it all round.
Ring size calculator: string or paper measurement
No ring to measure? Use this ring size measuring tool with a strip of paper or non-stretchy string. Wrap it snugly around the base of your finger, mark where it overlaps, then lay it flat on a ruler and enter the length.
Wrap snugly but not tight, mark the overlap with a pen, then measure from the end to the mark.
Measuring in inches? Divide by 0.03937, or use our inches to mm converter.
Printable ring sizer (actual size)
The printable ring sizer has two tools on one page: ring size circles from US 4 to 13 in half sizes, to place a ring on, and a ring sizer strip you cut out and wrap around your finger.
- Print at 100% / “Actual size”, never “Fit to page”.
- Check the 50 mm test line with a ruler before you measure. If it is not exactly 50 mm, the sizes will be wrong.
- A card should exactly cover the 85.6 mm card outline.
Opens a print-ready page. Choose “Save as PDF” in the print dialog to keep a copy.
Ring size chart in mm (US, UK and EU)
This ring size measurement chart converts between the main sizing systems. US sizes are based on inside diameter (US 0 = 11.63 mm, each full size adds 0.8128 mm). EU sizes follow ISO 8653, where the size number is the inside circumference in millimetres. Jewellers can vary slightly, so treat neighbouring half sizes as a range.
| US / Canada | UK / Australia | EU / ISO | Diameter (mm) | Circumference (mm) | Diameter (in) |
|---|---|---|---|---|---|
| 3 | F½ | 44 | 14.1 | 44.2 | 0.554 |
| 3½ | G½ | 45 | 14.5 | 45.5 | 0.570 |
| 4 | H½ | 47 | 14.9 | 46.8 | 0.586 |
| 4½ | I½ | 48 | 15.3 | 48.0 | 0.602 |
| 5 | J½ | 49 | 15.7 | 49.3 | 0.618 |
| 5½ | K½ | 51 | 16.1 | 50.6 | 0.634 |
| 6 | L½ | 52 | 16.5 | 51.9 | 0.650 |
| 6½ | M½ | 53 | 16.9 | 53.1 | 0.666 |
| 7 | N½ | 54 | 17.3 | 54.4 | 0.682 |
| 7½ | O½ | 56 | 17.7 | 55.7 | 0.698 |
| 8 | P½ | 57 | 18.1 | 57.0 | 0.714 |
| 8½ | Q½ | 58 | 18.5 | 58.2 | 0.730 |
| 9 | R½ | 60 | 18.9 | 59.5 | 0.746 |
| 9½ | S½ | 61 | 19.4 | 60.8 | 0.762 |
| 10 | T½ | 62 | 19.8 | 62.1 | 0.778 |
| 10½ | U½ | 63 | 20.2 | 63.3 | 0.794 |
| 11 | V½ | 65 | 20.6 | 64.6 | 0.810 |
| 11½ | W½ | 66 | 21.0 | 65.9 | 0.826 |
| 12 | X½ | 67 | 21.4 | 67.2 | 0.842 |
| 12½ | Z | 68 | 21.8 | 68.5 | 0.858 |
| 13 | Z+1 | 70 | 22.2 | 69.7 | 0.874 |
Need a millimetre value in inches? Use the mm to inches converter, see 20 mm to inches, or print the full mm to inches chart covering every mm from 1 to 300.
Tips for an accurate ring size measurement
- Measure at the end of the day. Fingers are usually larger in the evening and when warm, and smaller in the cold.
- Measure 3 times and use the average.
- Wide bands fit tighter. For bands wider than about 6 mm, many jewellers suggest going up half a size.
- Check the knuckle. The ring must slide over it. If your knuckle is much wider than the base of your finger, choose the size between the two.
- Between two sizes? Pick the larger one. A ring that is slightly loose is easier to fix than one that will not go on.
- Use the right finger. Your dominant hand is often half a size larger.
Where to buy a ring sizer
For an important purchase like an engagement ring, a physical ring sizer is the most reliable home option. A reusable plastic ring sizer tool (also called a ring size tester or ring measurer) costs about the same as a coffee and works like a belt: slip it on, pull it snug and read the size.
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Ring sizer FAQ
How do I find my ring size at home?
Measure a ring that already fits with the online ring sizer on this page, or wrap paper or string around the base of your finger, measure the length in mm and enter it in the ring size calculator. Measure three times at the end of the day and use the average.
Is an online ring sizer accurate?
Yes, if you calibrate it first. Screens show sizes differently, so this ring sizer tool asks you to match a standard 85.6 mm bank card on screen. After calibration it is usually accurate to about half a size. For an engagement ring, confirm with a physical ring sizer or a jeweller.
How do I use a printable ring sizer?
Print it at 100% or Actual size, never Fit to page, and check the 50 mm test line with a ruler. Then either place a ring on the circle that matches its inner edge, or cut out the ring sizer strip, wrap it around your finger and read the size where the start meets the strip.
What ring size is 17 mm?
A ring with a 17 mm inside diameter is about US size 6½, UK size M½ and EU size 53. The circumference is 53.4 mm.
What is the most common ring size?
Jewellers commonly report US 6 to 7 as the most common ring sizes for women and US 9 to 10 for men. Always measure, because finger sizes vary widely.
Should I size up for a wide band?
Often, yes. Bands wider than about 6 mm sit tighter on the finger, so many jewellers suggest going up half a size. If you are between two sizes, choose the larger one.
What is the difference between ring size by diameter and circumference?
Diameter is the distance straight across the inside of the ring. Circumference is the distance all the way round the inside, which equals the diameter multiplied by pi (about 3.14). US sizes are based on diameter, and EU sizes (ISO 8653) use the circumference in millimetres.
Where can I buy a ring sizer?
Reusable plastic ring sizers, also called ring size testers or ring measurers, are sold cheaply on Amazon and in craft and jewellery shops. They are the most reliable way to measure ring size at home.