Ring Size Ruler
Calibrate your screen with a card you already have, then drag a circle to match your ring's inner edge — your size updates live, no printer required.
Works best on desktop
How it works
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Grab a card or coin
A standard credit, debit, gift, or ID card (85.6 × 54mm worldwide) works best, or pick a common coin from the dropdown.
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Calibrate your screen
Hold it against the box below and drag the calibration slider until the box matches it exactly.
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Match your ring
Place a ring that fits flat on the screen over the circle — or hold it up to the screen — and drag the diameter slider until the circle matches its inner edge.
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Read your size
Your diameter, circumference, and US, UK, EU, and Japan sizes update instantly as you drag.
Step 1 — Calibrate your screen
Pick what you're using below, hold it up to the screen against the box, then drag the slider until the box matches it exactly.
Step 2 — Match your ring
Place a ring over the circle, or hold it up to the screen, then drag the slider until the circle's edge matches the ring's inner edge.
Diameter
17.3 mm
Closest size
US 7
UK / AU
N 1/2
EU
54
Japan
14
Circumference
54.3 mm
Calibrate before you measure
When to see a jeweler
Frequently asked questions
Why do I need to calibrate first?
Browsers size on-screen measurements off a 96-DPI reference that rarely matches your screen's actual pixel density. A standard card (ISO/IEC 7810 ID-1, 85.6 × 54mm) or a common coin is a reliable reference almost everyone has on hand, so calibrating against one corrects for your specific screen before you measure anything.
What if I don't have a card?
Use the dropdown to switch to a coin instead — a US quarter, 1 euro, UK £1, or CA $1 loonie are all supported. If you have none of those, hold a ruler up to the screen and drag the calibration slider until the box's edge lines up with its labeled size in millimeters. A US dollar bill (155.96mm long) or a AA battery (14.5mm diameter) also work as rough references in a pinch.
Which edge of the ring should I match?
The circle represents the ring's inner diameter — the hole your finger goes through, not the outer edge of the band. Line up the circle's edge with the inside edge of the ring.
How accurate is this compared to printing?
Once calibrated, it's close — but small errors (a card held slightly off the screen, screen bezels, calibrating by eye) can shift the result by a quarter size or so. For a second opinion, try the Printable Ring Sizer or measure an existing ring with a physical ruler in the Ring Size Calculator.
My calibration percentage is way off from 100% — is that normal?
Yes. High-resolution phone and laptop screens often need a calibration value well below or above 100% because their actual pixel density differs significantly from the 96-DPI reference browsers assume. As long as the box matches your card, the percentage itself doesn't matter.
What should I do with my result?
Treat it as a strong starting point. If you're between two sizes, size up — it's cheaper and easier for a jeweler to make a ring smaller than bigger. Confirm with a jeweler before buying anything permanent or hard to resize.
Go further
Double-check your result or fine-tune for fit.