728 × 90 Leaderboard

320 × 100 Mobile Banner

Ring Size Calculator

Convert ring sizes between US, EU, UK, and mm diameter.

Last updated: June 13, 2026

Calculator

Inner Diameter

Results

US Ring Size7.9

Circumference56.5 mm

Diameter18.0 mm

EU Size57

How to Use This Calculator

1Measure the inner diameter of a ring that fits.
2Enter the diameter in millimeters.
3View US, EU, and UK ring sizes.

Formula Explanation

Ring size is calculated from the inner circumference of the ring. US sizes are based on a formula relating circumference to size number.

Circumference = π × Diameter US Size = (Circumference - 36.5) ÷ 2.55

Variables:

DiameterInner ring diameter in mm

CircumferenceInner circumference in mm

Worked Examples

18mm inner diameter

1. Circumference = π × 18 = 56.5 mm
2. US size = (56.5 - 36.5) / 2.55 = 7.8

Result: Approximately US size 8

Why Use This Calculator

Find your ring size at home.
Convert between sizing systems.
Order rings online confidently.
Measure existing rings for surprise gifts.

336 × 280 Large Rectangle

300 × 250 Medium Rectangle

Tips & Best Practices

Measure an existing ring that fits well for the most accurate size.
Fingers swell in heat and shrink in cold — measure at room temperature.
The average US women's ring size is 6-7; men's is 9-10.
When in between sizes, order the larger size — it's easier to size down.

Common Mistakes to Avoid

❌ Measuring finger circumference instead of ring diameter.

✅ If measuring your finger with string, that gives circumference. Divide by π (3.14) to get diameter, or use the circumference directly to find your size.

❌ Measuring the wrong finger.

✅ Ring fingers on each hand are often different sizes. Measure the exact finger you plan to wear the ring on.

Frequently Asked Questions

How do I measure my ring size at home?

Wrap a strip of paper or string around your finger, mark where it overlaps, and measure the length in mm. That's your circumference. Divide by 3.14 for diameter.

Do ring sizes change?

Yes. Weight gain/loss, temperature, time of day, and pregnancy can all affect ring size by 0.5-1 full size.

336 × 280 Large Rectangle

300 × 250 Medium Rectangle

Embed This Calculator

Add the Ring Size Calculator to your website for free. Copy the code below and paste it into your HTML.

Width

Height

<iframe src="https://redicalc.com/embed/travel/ring-size-calculator" width="100%" height="600" style="border:none;border-radius:12px;box-shadow:0 1px 3px rgba(0,0,0,0.1);" title="Ring Size Calculator — RediCalc.com" loading="lazy" allowtransparency="true"></iframe>

Preview embedFree to use · Attribution link included

Disclaimer: This calculator is provided for informational and educational purposes only. Results are estimates and should not be used as a substitute for professional advice. RediCalc.com makes no guarantees regarding the accuracy, completeness, or suitability of any calculations. Always consult a qualified professional before making financial, health, construction, or other important decisions.

160 × 600Skyscraper