You've found the ring. Now you need a number, and the jeweler's counter is either closed, three states away, or simply not where you want to buy from. Every "how to find your ring size" article online repeats the same string-and-ruler trick, buries it under ads, and sends you off with a generic size chart and zero plan for what to actually do once you have a number. None of them tell you that the string method's real accuracy ceiling is about half a size, or what to do with that uncertainty once you're comparing the same ring across five different jewelers.
This guide covers the measuring method that actually works at home, a complete US-UK-EU-diameter conversion chart, the specific mistakes that quietly add or subtract half a size from your result, and — once you have a number you trust — how to save and compare rings from multiple stores and preview them on your own hand with AI try-on before you buy, using a cross-store wishlist like Spree.
Why Guessing Your Ring Size Goes Wrong
There is no single "ring size" the way there's a single foot length. Finger size shifts by several factors most people never account for — the time of day, the temperature of the room, even which specific finger on which hand. A measurement taken on a cold morning, compressed too tightly, or taken on the wrong finger can be off by a full size before you even open a conversion chart. That's exactly why so many rings bought as surprise gifts, or ordered from out-of-state jewelers, come back for a resize.
01
Time of day
Fingers swell slightly over the course of a normal day — a morning measurement and an evening measurement on the same hand can differ by a quarter size.
02
Temperature
Cold hands shrink; warm hands swell. Measuring right after being outside in winter or right after a hot shower both skew the result.
03
Wrong finger, wrong hand
Your dominant hand is often slightly larger, and no two fingers on the same hand are the same size — measure the exact finger the ring will actually sit on.
04
Band width
A wide band (6mm+) touches more of your finger than a thin one, and typically needs a quarter to half size larger than a thin band at the identical circumference.
The String-and-Chart Method: How to Measure at Home
You'll need a thin strip of paper (or a piece of non-stretchy string or dental floss), a pen, and a ruler that shows millimeters. The whole thing takes under five minutes.
1
Pick the right time and finger
Measure in the evening, at normal room temperature, on the exact finger the ring will be worn on. If it's a surprise gift, borrow a ring the person already wears on that finger instead and measure its inside diameter.
2
Wrap the strip around your finger
Wrap the paper strip or string snugly around the base of your finger — snug enough that it doesn't slide over your knuckle, but not pulled tight enough to compress the skin.
3
Mark the overlap point
Mark exactly where the strip overlaps itself with a pen, then lay it flat against your ruler and measure the distance from the start to that mark in millimeters. That number is your finger's circumference.
4
Match it to a size chart
Use the circumference (not diameter — dividing by pi is a common mistake that produces the wrong number) against the conversion chart below to find your US, UK, and EU size.
5
Adjust for band width
If the ring you're ordering has a wide band (6mm or more), size up a quarter to half size from what the chart gives a thin band — wide bands fit tighter than their number suggests.
Ring Size Conversion Chart: US, UK, EU, and Diameter
The US and Canada use a numeric scale, the UK and Australia use letters, and most of the EU and Japan size by the internal circumference in millimeters directly. Match your measured circumference to the closest row below.
| US |
UK / AU |
EU |
Diameter (mm) |
Circumference (mm) |
| 5 | J½ | 49 | 15.7 | 49.3 |
| 5.5 | K½ | 50 | 16.1 | 50.6 |
| 6 | L½ | 51.5 | 16.5 | 51.9 |
| 6.5 | M½ | 53 | 16.9 | 53.1 |
| 7 | N½ | 54 | 17.3 | 54.4 |
| 7.5 | O½ | 55.5 | 17.7 | 55.7 |
| 8 | P½ | 57 | 18.1 | 57.0 |
| 8.5 | Q½ | 58 | 18.5 | 58.3 |
| 9 | R½ | 59.5 | 18.9 | 59.5 |
| 9.5 | S½ | 61 | 19.4 | 60.8 |
| 10 | T½ | 62.5 | 19.8 | 62.1 |
Treat this chart the same way you would a clothing size conversion chart: a reliable starting point, not a guarantee, since some jewelers round their internal charts slightly differently.
What to Do Once You Know Your Size
A size number tells you which box to check at checkout — it doesn't tell you which ring, from which store, actually looks right on your hand. That's a different problem, and it's the one a cross-store wishlist with AI try-on is built for.
1
Save candidates from any jeweler
Get Spree from the App Store, then paste the product URL or share it in from any of 1,000+ stores — the photo and price come along automatically.
2
Compare them in one wishlist
Put the rings you're deciding between into one cross-store wishlist instead of a dozen open tabs, and swipe to narrow them down.
3
Preview it on your own hand
Use AI Virtual Try-On on your own photo to see how the ring actually reads against your hand before you commit — a product photo on a stock model tells you far less.
Shoppers who used virtual try-on before buying returned items 36% less often (McKinsey, 2025) — fewer obvious mismatches reaching checkout, on jewelry just as much as clothing.
If you're still working out your measurements for an order beyond rings, how to measure yourself for online shopping covers the rest of the body the same way this guide covers your finger.
Frequently Asked Questions
How can I find my ring size at home without a ring sizer?
+
Wrap a thin strip of paper or string snugly around the base of your finger, mark where it overlaps, then measure that length against a ruler in millimeters. Match the number to a ring size chart to get your size. It's not as precise as a metal sizer from a jeweler, so treat the result as a strong starting point and size up slightly for wider bands.
Is the string or paper method actually accurate?
+
It's accurate enough to get within half a size for most people, which is usually close enough to order with confidence, but it isn't lab-precise. String can stretch slightly, paper can compress, and a few millimeters of error is common. For a wedding band or an expensive piece, a $5 plastic ring sizer or an in-person jeweler measurement is worth the extra step.
What's the best time of day to measure my ring size?
+
Measure in the evening when your fingers are at their largest from normal daily swelling, and avoid measuring right after exercise, in the cold, or first thing in the morning when fingers tend to run smaller. Measuring at a "middle of the day" body temperature gives the most realistic everyday size.
Do ring sizes differ between US, UK, and EU?
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Yes. The US and Canada use a numeric scale (like 6 or 7), the UK and Australia use letters (like M or N), and most of the EU and Japan measure the internal circumference in millimeters directly. A US size 7 is roughly a UK size N and an EU/circumference size of about 54mm - always check the specific store's own chart, since small rounding differences exist between retailers.
Does Spree help with ring sizing?
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Not by measuring your finger - Spree is upfront about that. Its job starts once you have a size: save rings you're considering from any store into one wishlist, compare them side by side, and use AI Virtual Try-On on your own photo to see how a ring actually looks on your hand before you order. It won't give you a size number, but it's the best way to narrow down which ring to size for in the first place.
The Bottom Line
Finding your ring size at home is a solved problem — a strip of paper, a ruler, and a conversion chart get you within half a size, which is close enough to order with real confidence. The time of day, the temperature of the room, and the width of the band are the quiet variables that actually matter more than which chart you use.
Once you have that number, the harder decision is usually which ring, from which store, actually looks right — and that's where comparing real candidates from different jewelers side by side, and previewing each one on your own hand with AI try-on, saves far more regret than the measuring step ever did.