How to Measure Ring Size at Home: Five Methods, Ranked by Accuracy
Wrap, mark, measure, repeat. Here is the method step by step, then the five ways to measure ranked by accuracy, and the timing and fit checks that stop you ordering the wrong size.
The author is the founder of Draco Diamond, which mails a free plastic ring sizer to Canada and the United States. Measuring guidance comes from GIA and the NHS, cited below. Conversions use the published US size scale. Read October 18, 2026.
How do you measure ring size at home?
Wrap a thin strip of paper or string around the base of the finger, mark where it overlaps, and measure the length in millimetres. Match that length to a size chart, and repeat at the end of three different days.
Use string that does not stretch, dental floss or a strip of paper about 5 mm wide. A narrow strip sits where a band will sit.
Wrap it around the base of the finger you are sizing. It should be snug without pressing into the skin.
Mark where the end meets the strip with a fine pen. A thick marker can shift the reading on its own.
Lay the strip flat against a ruler and read the length to the nearest millimetre. That length is the inside circumference.
Find the length on a size chart: 54.4 mm is a US size 7. Then check that a ring of that size would pass over the knuckle.
Take three readings at the end of three different days. If they disagree, choose the larger size that still feels snug.
The ruler is the weak link. Most rulers mark whole millimetres, and one millimetre is close to 40 percent of a size. Read the mark at eye level, not from an angle.
A size chart turns the length into a size. Our ring size chart lists every US and Canadian size from 3 to 13 in millimetres, with UK, Australian and European equivalents.
Mark the strip where it overlaps, not where it ends. Cut it at the mark only after you have checked the reading twice.
Which home method is the most accurate?
A rigid tool beats a flexible one. From most to least reliable, the options are a jeweller's finger gauges, a plastic sizer, a ring that already fits, a printed sizer, and string or paper.
| Method | What it measures | Main risk | Reliability |
|---|---|---|---|
| Jeweller's finger gauges | The finger, one size at a time | Needs a visit | Highest |
| Plastic ring sizer | The finger, with a rigid band | Reading the wrong mark | High |
| A ring that already fits | The ring's inside diameter | A band out of round | Good |
| Printed paper sizer | The finger, with paper | Printer scaling | Fair |
| String or paper strip | The finger's circumference | Stretch, tears, slack | Lowest |
Finger gauges come first. A set of gauges, one ring per size, is the most accurate way to find a ring size. Plastic sizers give a fairly accurate measurement.2
String and paper come last. String can stretch, and paper can be easily damaged. Both still work as a first estimate, if you repeat them.2
A ring that already fits sits in the middle. Metal does not stretch, so its inside diameter is a firm number. The catch is shape: the inside must be perfectly round.3
Printed sizers depend on the printer. If the page scales even slightly, every size on it shifts. Print at 100 percent, then check the printed scale against a ruler before you cut.
The order is Draco's ranking, built from that guidance. It puts the methods you can do tonight in their honest place: useful, but not final.
A ring that already fits gives a better reading
If you own a ring that fits the same finger, measure the ring instead of the finger. A metal band does not stretch, and its inside diameter converts straight to a size.
Lay the ring on a ruler and measure the inside, edge to edge, through the centre. 17.3 mm is a US and Canadian size 7. Each whole size adds 0.81 mm.
Measure the inside, not the outside. A band 1.5 mm thick adds 3 mm across the outside, close to four sizes.
The ring has to be round. A band knocked out of shape gives a false reading, and the inside must be perfectly round for this method to work.3
Use a ring from the same finger on the same hand. A ring from the middle finger, or from the other hand, measures a different finger.
When should you measure your finger?
Measure at the end of the day, at a comfortable room temperature. Fingers change with heat, cold and time, and a morning reading can run small.
A reading taken on a cool morning can differ from one taken in the afternoon, as the temperature rises.2
Cold shrinks fingers and heat swells them. Avoid measuring straight after a hot shower, a workout or a cold walk outside.
Pregnancy changes the reading. Swelling in the fingers is normal in pregnancy, and it is often worse at the end of the day and later in pregnancy.4
A sudden increase in swelling is different. It can be a sign of pre-eclampsia and needs a call to a midwife or doctor, not a jeweller.4
If a ring is for an engagement during pregnancy, size for comfort now and plan a resize later. Draco includes one complimentary resize within 60 days of delivery.5
"Half a ring size is 1.3 millimetres of string. Measure three times, at the end of the day, and the margin takes care of itself."
Garrett McMartin, Founder, Draco Diamond
Take three readings on three different days, at the same time of day. If one is out of line, set it aside and trust the other two.
Knuckles, wide bands and the other hand change the size
A size that fits the base of the finger is only half the answer. The ring also has to clear the knuckle, suit the band width and match the hand it will be worn on.
Check the knuckle. Slide the strip or the sizer over the knuckle before you settle on a size. If it will not pass, the ring will not either.
If the knuckle is much larger than the base, a ring sized for the knuckle may spin. A jeweller can fit small beads or a bar inside the band to hold it upright.
Wide bands fit tighter. Rings with wide shanks usually need to be a bit larger, because they fit more snugly.2
Band profile matters too. A comfort fit band, rounded on the inside, can feel looser than a flat band of the same size. If you can, measure in a band like the one you are buying.
Size the right hand. The left ring finger is typically smaller than the right by about half a size. Measure the finger the ring will live on.2
Between two sizes, choose the larger. It is easier to remove metal from a ring that is too big than to add metal to one that is too small.2
Half a ring size is 1.3 millimetres, so small slips matter
Ring size is a small measurement with a small margin. On the US and Canadian scale, each whole size adds 2.55 mm to the inside circumference. Half a size is about 1.3 mm.
The scale dates to a 1921 US Bureau of Standards circular. Each whole size adds 0.032 inch, or 0.8128 mm, to the inside diameter. Multiply by pi and you get the 2.55 mm around.1
Half a size is 1.3 mm around and 0.4 mm across
Millimetres on the US and Canadian scale. String and paper measure around the finger; a ruler across a ring measures the diameter.
Source: the US ring size scale, 0.032 inch of inside diameter per whole size, via Wikipedia's ring size entry. Arithmetic: Draco Diamond.
So a pen mark that lands 1.3 mm too far along a string reads half a size large. A paper strip pulled a little tight reads half a size small. The finger has not changed. The method has.
Half a size matters more than it sounds. A ring half a size small will fight the knuckle. A ring half a size large can spin, turning the centre stone toward the palm.
That is the case for two habits. Measure more than once, and use a rigid tool when you can. Both are covered in the sections above.
A free plastic sizer removes the guesswork
Draco mails a plastic ring sizer free to addresses in Canada and the United States. It gives a rigid reading at home, without string, a printer or a borrowed ring.
Request it below with your name, email and postal address. Each request receives an email confirmation, and the sizer follows by mail.
Use it the way this guide describes. Measure at the end of the day, on the finger the ring will be worn on, three times. Check that the size clears the knuckle.
Then order with a margin behind you. Every Draco ring includes one complimentary resize within 60 days of delivery, up to two sizes up or down. You cover shipping to us, and Draco covers the return trip.5
Some ring designs cannot be resized, and Draco discloses this before purchase.5
Every Draco piece carries 30 day returns, the Lifetime Authenticity Guarantee, free resizing, and free insured worldwide shipping to 25 markets, delivered duty paid with nothing collected at the door, and signature on delivery. Each piece is IGI certified, E to F colour and VS2 or better, with a report you can verify free at IGI.org.
Browse women's rings and lab grown diamond engagement rings, or build your own ring.
Sizing, answered
Can you measure ring size at home accurately?
Yes, to within about half a size, if you use a rigid method and repeat it. A plastic sizer or a ring that already fits is more reliable than string or paper. Measure at the end of the day and check that the size clears the knuckle.
Is ring size the circumference or the diameter?
Both describe the same size. String and paper measure the inside circumference, and a ruler across a ring measures the inside diameter. A US and Canadian size 7 is 54.4 mm around and 17.3 mm across.
How do I measure ring size with a string?
Wrap string that does not stretch around the base of the finger, mark where it overlaps and measure the length in millimetres. Convert the length with a size chart. Half a size is only about 1.3 mm of string, so repeat it on three different days.
Should I size up or down if I am between sizes?
Size up. It is easier for a jeweller to remove metal from a ring that is too big than to add metal to one that is too small. Wide bands also need a little more room.
Is my ring size the same on both hands?
Often not. The left ring finger is typically about half a size smaller than the right. Measure the finger the ring will be worn on.
How do I get a free ring sizer?
Draco mails a plastic ring sizer free to addresses in Canada and the United States. Request it on this page with your name, email and postal address.
References
- Wikipedia, Ring size, accessed October 18, 2026.
- GIA 4Cs, How to Determine Ring Size: Tips and Ring Size Chart, January 18, 2018.
- Gemological Institute of America, Accurate Determination of Finger and Ring Sizes, accessed October 18, 2026.
- NHS, Swollen ankles, feet and fingers in pregnancy, April 19, 2024.
- Draco Diamond, Refunds, Integrity and Ethical Standards, accessed October 18, 2026.
Send us a comparable band and we will beat it almost every time
Same IGI certified specification, direct pricing, about half the listed price of Blue Nile and Brilliant Earth on bridal sets (55 percent below at the median, October 2026). Founder reviewed, no obligation, a quote back in one to three business days. Every Draco band is IGI certified, E to F colour, VS2 and better, with 30 day returns, a Lifetime Authenticity Guarantee, free resizing, free insured worldwide shipping to 25 markets, and signature on delivery.
