Ring Sizer
Lay an existing ring on the screen, or match a circle to your finger. Get the size in US, UK/AU, EU/ISO mm and JP at once.
Free core
Coming soon · in App Store review
Mesurix
A measuring instrument, not a gadget.
Find your ring size, square up a shelf with a real ruler, true up a frame with a level — all measured precisely on your iPhone. Calibrate the screen once against any bank card and every reading is honest, local math. No account. No cloud. The core is always free.
Coming soon — Mesurix is in App Store review.
Free online ring sizer · no download
Measure your ring size right here
Try it in your browser: calibrate the screen with any bank card, then size a ring you already own. For UK and JP sizes, saved profiles, finger-measure and a printable sizer, get the Mesurix app.
Step 1
Calibrate your screen
Every bank or ID card is exactly 85.60 mm wide. Hold one flat against the screen and drag the slider until the outline matches its width exactly.
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Step 2
Size your ring
Lay a ring that already fits flat on the screen and drag until the gold circle matches the inner edge you can see through the band.
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US 7
17.3 mm inner Ø
EU/ISO 54
Between sizes? Choose the larger — a ring must clear the knuckle. This is an estimate; for an expensive ring, confirm with a jeweller.
Three instruments, one app
What you can measure
Version one ships with the three tools people reach for most. Each works entirely offline, with no per-use cost and no sign-in — and each is part of the free core.
On-screen Ruler
A real, card-calibrated ruler in millimetres and inches — accurate to the pixel on your specific display.
Free coreBubble Level
A spirit level driven by the phone's motion sensors. Hang a frame, set a shelf, true up a tabletop in seconds.
Free core
Ring sizer
Know your ring size before you buy
Already own a ring that fits? Lay it flat on the screen and scale the circle to the inner edge — Mesurix reads the inner diameter to a tenth of a millimetre and turns it into a real size. No ring handy? Match the circle to your finger instead.
- Place-a-Ring and Finger Measure methods
- Results in US, UK/AU, EU/ISO (mm) and JP
- "Between sizes" guidance — a ring must clear the knuckle
- Printable paper sizer as a backup
On-screen ruler
A ruler that fits in your pocket
Calibrated to your exact display, the Mesurix ruler measures small objects in millimetres, centimetres or inches — with a clear zero line so you measure from the right place, not the screen edge. A movable guide marks any length you need to keep.
- mm / cm and inches, switchable in a tap
- True-to-scale on your specific iPhone
- Fine-tune to 0.1 mm and copy the value
- Honest about its limit — it tells you the longest length it can show
Bubble level
Straighten anything, anywhere
A bullseye spirit level that uses your phone's motion sensors. Read the tilt on both axes in degrees, and tap Set zero on a known-flat surface to cancel out normal sensor bias — the same trick a tradesperson uses to true a level.
- Live X and Y tilt in degrees
- Bullseye and surface modes
- One-tap calibration for accurate readings
- Works fully offline, no permissions beyond motion
Calibrate once, measure for good
How Mesurix works
The trick to measuring on a phone is scale. Every screen has a different pixel density, so Mesurix anchors to something everyone already carries: a bank card.
01
Calibrate to a card
Place any bank or ID card on the screen and align the outline. Every card is exactly 85.60 mm wide by ISO standard — a free, universal ruler.
02
Measure
Pick a tool. Scale the circle to your ring or finger, drag the ruler, or rest the phone to read a level. Everything updates live, on-device.
03
Read & save
See your result in every standard, print a paper sizer, copy a value, or save the size to a named profile for next time.
Why it earns your trust
Precision you can verify
On-device
Every measurement is local math. Nothing is uploaded.
No account
No sign-in, no profile, no tracking of who you are.
Card-calibrated
Scaled to the ISO 85.60 mm card — a universal physical ruler.
Free core
Measuring is never paywalled. Pro only adds breadth.
The guide
How to measure your ring size at home
Ring sizing is just one number: the inner diameter of the band, in millimetres. Every regional system — US numbers, UK and Australian letters, the EU/ISO millimetre standard, Japanese sizes — is a different label for that same circle. Mesurix measures the circle and prints all the labels, so you can buy with confidence wherever the ring comes from.
The most reliable way to size at home is the Place-a-Ring method: take a ring that already fits the right finger, lay it on the calibrated screen, and scale the on-screen circle until it matches the inner edge you can see through the band. If you don't have a ring to copy, the Finger Measure method grows a circle to the base of your finger instead.
A few tips for an accurate result
Measure at the end of the day, when fingers are at their largest, and avoid sizing when you are cold — fingers shrink. If a ring sits oval rather than round, fit the circle to the widest span. And when you fall between two sizes, choose the larger one: a ring has to pass the knuckle to get on and off.
Ring size conversion chart
Approximate inner diameter for common sizes. Mesurix shows the precise value for your exact measurement.
| Inner Ø (mm) | US | UK / AU | EU / ISO | JP |
|---|---|---|---|---|
| 15.7 | 5 | J½ | 49 | 9 |
| 16.5 | 6 | L½ | 52 | 11 |
| 17.3 | 7 | N½ | 54 | 13 |
| 18.1 | 8 | P½ | 57 | 16 |
| 18.9 | 9 | R½ | 59 | 18 |
| 19.8 | 10 | T½ | 62 | 20 |
| 20.6 | 11 | V½ | 65 | 22 |
| 21.4 | 12 | X½ | 67 | 24 |
Chart values are rounded for reference. For a purchase, measure with Mesurix and, for high-value rings, confirm with a jeweller.
Questions
Frequently asked
How does Mesurix measure my ring size?
You calibrate the screen once against any standard bank or ID card, then either lay an existing ring on the screen and scale a circle to its inner edge, or match a circle to your finger. Mesurix converts the inner diameter into US, UK/AU, EU/ISO (mm) and JP ring sizes.
Is the ring sizer accurate?
Accuracy depends on careful screen calibration and steady placement. Mesurix calibrates against the ISO standard card width (85.60 mm), a universal physical reference, and reads to a tenth of a millimetre. For an expensive purchase, confirm the result with a jeweller.
Do I need an internet connection or an account?
No. Mesurix works entirely on your device. There is no sign-in and no cloud — every measurement is local math and your results never leave your phone.
Is Mesurix free?
Yes. The core — ring sizer, on-screen ruler and bubble level — is always free. An optional Pro subscription adds convenience such as viewing all size standards side by side and saving multiple sizes and profiles.
What ring size standards does it support?
US numeric, UK/AU letter, EU/ISO in millimetres, and Japanese (JP) sizes, shown together for Pro users.
Which devices does Mesurix support?
Mesurix is built for iPhone, with Android support planned. It uses your screen for the ruler and ring sizer, and your device's motion sensors for the level.
Be first to measure with it
Mesurix is on its way to the App Store and Google Play.