The most accurate way to measure your ring size at home is to measure a ring that already fits. Lay it on your phone with the on-screen ring sizer, or measure its inside diameter with a ruler. If you have no ring, wrap a strip of paper around your finger and look up the length. Both take less than five minutes; the details below show how to avoid the half-size errors most people make.
On this page (9 sections)
- Which method should you use?
- Method 1: On your phone screen
- Method 2: Measure a ring with a ruler
- Method 3: String or paper strip around your finger
- Method 4: Printable ring sizer
- Method 5: A plastic ring sizer
- Tips for an accurate result
- Measuring someone else’s ring size secretly
- Frequently asked questions
Which method should you use?
| Method | You need | Typical accuracy | Best for |
|---|---|---|---|
| 1. On-screen sizer | Phone + bank card (or a coin) + a ring | About ±¼ size (designed for) | Fastest, no tools |
| 2. Ring + ruler or caliper | A ring + mm ruler | ±½ size (ruler), ±¼ (caliper) | When you have a ruler |
| 3. Paper strip or string | Paper / thread + ruler | ±½ size | No ring that fits |
| 4. Printable sizer | Printer + ruler | ±½ size | Measuring away from a screen |
| 5. Plastic ring sizer | Reusable sizer belt | ±½ size | Measuring several people |
Method 1: On your phone screen
- Open the ring sizer on your phone.
- Hold any bank, debit or ID card against the screen and drag the slider until the outline matches the card. On a phone, hold the card upright and match its short side (53.98 mm); on a computer, match its long side (85.6 mm). All these cards are the same size, so this tells the tool the true size of your screen. No card? Tap No card? Use a coin and match a ₹10, Rs 10, quarter, 10p or €2 coin (a card is more accurate).
- Lay a ring that fits the right finger flat on the screen and adjust the circle until it lines up with the inside edge.
- Read your US, UK, EU, Indian size and the diameter in mm.
Example: the circle matches the ring at 17.7 mm, so the size is US 7.5 / UK O½.
Tap Save to keep the size on your phone for each person and finger, and use Will it fit? to check a size a shop lists before you order.
Method 2: Measure a ring with a ruler
- Put the ring on a ruler with millimetre marks.
- Measure straight across the centre, from inside edge to inside edge.
- Measure again at right angles and take the average, since rings are rarely perfectly round.
- Enter the number in the ring size calculator or find it in ring size by diameter.
Example: 18 mm one way and 18.2 mm the other gives 18.1 mm, which is US 8 / UK P½. A digital caliper (inside jaws) gives 0.1 mm readings and is the most accurate home tool.
Method 3: String or paper strip around your finger
- Cut a strip of paper about 5 mm wide and 10 cm long. Paper stretches less than string; if you use thread, choose non-stretch sewing thread or dental floss.
- Wrap it around the base of the finger, snug but not tight. It must still slide over the knuckle.
- Mark the point where the end overlaps with a fine pen.
- Lay it flat on a ruler and measure to the mark in millimetres. This is your finger circumference.
- Look it up in ring size by circumference, or divide by 3.1416 for the diameter.
Example: the strip measures 59.5 mm. 59.5 ÷ 3.1416 = 18.9 mm diameter, closest to US 9 / UK R½ / EU 60.
Repeat three times. If the readings differ by more than 1.5 mm, you pulled harder on one of them; use the middle value.
Method 4: Printable ring sizer
Download the free printable ring sizer, print at 100% and check the 50 mm line with a ruler. Then match a ring to the true-size circles or use the cut-out finger strip. This is a good option if you need to measure someone else’s ring without a phone nearby.
Method 5: A plastic ring sizer
Reusable plastic sizer belts cost very little and work like a small belt: thread the end through, tighten and read the size. They are handy for a quick check, but they are less reliable than a jeweller’s metal ring sizers: the strip can be pulled too tight or sit at an angle, so read it twice and treat it as within about half a size. Make sure the one you buy uses the same system as the shop (US numbers or UK letters).
Tips for an accurate result
- Time of day: measure in the late afternoon or evening. Fingers are smallest in the morning.
- Temperature: cold makes fingers shrink, heat and exercise make them swell. Measure at normal room temperature.
- Right finger, right hand: the dominant hand is often ¼ to ½ size larger.
- Knuckles: if your knuckle is much bigger than the base of the finger, measure both and choose a size between them.
- Wide bands: for bands 6 mm or wider, go up ¼ to ½ size.
- Between two sizes: choose the larger one. A ring that is slightly loose can be fitted with a sizing bead; one that will not pass the knuckle cannot be worn.
Measuring someone else’s ring size secretly
For a surprise engagement ring, borrow a ring they wear on the same finger and measure it on your phone with the ring sizer or with a ruler, then put it back. If you can only borrow a ring from another finger, remember that the ring finger is usually about half a size smaller than the middle finger. Most women wear US 5 to 7 and most men US 8 to 11, but buy from a jeweller that offers free resizing in case you are off.
More ideas, from tracing a ring to asking a friend: how to find out someone’s ring size secretly.
Not sure of your ring size? Measure it on your phone screen in 30 seconds.
Open the free ring sizer →Frequently asked questions
How can I measure my ring size without a measuring tape?
Wrap a strip of paper around your finger, mark the overlap and measure the strip against any ruler, or skip the ruler entirely: put a ring that fits on your phone and use the on-screen ring sizer, calibrated with a bank card.
Is measuring ring size with string accurate?
String can stretch and is easy to pull too tight, so it is usually accurate to about half a size. Non-stretch thread, dental floss or a paper strip give better results. Measure three times and use the middle value.
What finger size is average for a woman?
Most women wear US 6 to 7 on the ring finger, which is 16.5 to 17.3 mm in diameter, UK L½ to N½.
Should a ring be tight or loose?
It should slide over the knuckle with a little resistance and not spin freely at the base of the finger. If it leaves a deep mark or is hard to remove, it is too tight.
Does ring size change over time?
Yes. Weight change, pregnancy, age and arthritis can all change finger size, so measure again before buying a new ring rather than relying on a size from years ago.
Sources and standards
- ISO 8653:2016 – Jewellery – Ring-sizes – Definition, measurement and designation: defines ring size as the inner circumference in mm (EU sizes).
- UK / Australian ring letter scale (customary): based on the withdrawn BS 6820:1987; rings are measured per BS EN ISO 8653.
- NIST – SI units: length: 1 inch = 25.4 mm exactly, used for every inch-to-mm conversion.
The formulas and rounding rules are on our how we measure page.