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O-Ring Diameter Calculator

Use our interactive O-ring calculator to help select the optimum size O-ring to use, in accordance with the principles within ISO 3601.

Visual Ring Sizer

Adjust the slider to match your ring or finger size

⌀ 16.5 mm
11 mm31 mm

Your Ring Size

IN
10
US
6
UK
L
EU
52
JP
10

Diameter: 16.5 mm

Circumference: 51.9 mm

Most accurate method • Includes 50mm calibration line

Professional Tips

Best Time to Measure

Measure at the end of the day when fingers are largest.

Temperature Matters

Cold weather makes fingers smaller, warm weather makes them larger.

Ring Width Consideration

Wide bands (6mm+) may need to be ½ size larger than thin bands.

Knuckle Check

Ring should slide over knuckle with slight resistance.

Measure Multiple Times

Take 2-3 measurements to ensure accuracy.

Professional Fitting

When in doubt, visit a professional jeweler for accurate sizing.

Complete Ring Size Chart

Diameter (mm)Circumference (mm)INUSUKEUJP
14.144.343F444
14.545.653.5G45.55
14.946.864H46.56
15.348.174.5I487
15.749.385J49.58
16.150.695.5K50.59
16.551.9106L5210
16.953.1116.5M5311
17.354.4127N54.512
17.755.7137.5O55.513
18.157.0148P5714
18.558.3158.5Q58.515
18.959.5169R59.516
19.461.0189.5S6117
19.862.21910T6218
20.263.52010.5U63.519
20.664.72111V6520
21.066.02211.5W6621
21.467.22312X67.522
21.868.52412.5Y68.523
22.269.72513Z7024
22.671.02613.5Z+17125
23.072.32714Z+27326
23.473.52814.5Z+37427
23.874.82915Z+47528
24.276.03015.5Z+57629
24.677.33116Z+67730
25.078.53216.5Z+77931
25.479.83317Z+88032
25.881.13417.5Z+98133
26.282.33518Z+108234
26.683.63618.5Z+118435
27.084.83719Z+128536
27.486.13819.5Z+138637
27.887.33920Z+148738
28.288.64020.5Z+158939
28.689.84121Z+169040
29.091.14221.5Z+179141
29.492.44322Z+189242
29.893.64422.5Z+199443
30.294.94523Z+209544

For best accuracy, use the printable sizer or visit a jeweler. Measure in the evening when fingers are largest.

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Find Your Perfect Ring Size Instantly & Accurately

Our Free online Ring Size Calculator offers multiple measurement methods including visual sizer, diameter, circumference, international converter, and quick finder. Supports India, US, UK, EU, and JP standards – no jeweler visit needed!

What is a Ring Size Calculator?

A ring size calculator is a digital tool that helps you determine your exact ring size using various measurement methods including visual comparison, diameter measurement, circumference measurement, or size conversion.

Our advanced version offers 5 different methods for maximum accuracy: Visual Sizer (interactive slider), Diameter Method (measure existing ring), Circumference Method (measure finger), International Converter (convert between systems), and Quick Finder (personalized recommendations).

Why Choose Our Ring Size Calculator?

Get professional-level accuracy from home with multiple measurement options. Perfect for surprise proposals, online shopping, or confirming sizes across 5 international standards (India, US, UK, EU, JP).

Key Features & Benefits

Here's what makes our tool the best choice:

  • 5 measurement methods: Visual Sizer, Diameter, Circumference, Converter, Quick Finder
  • Support for 5 sizing systems: India, USA, UK, Europe, and Japan
  • Interactive visual ring sizer with real-time adjustment
  • International size converter between all systems
  • Quick Finder with personalized recommendations based on finger type and ring style
  • Free printable PDF sizer with 50mm calibration line
  • No login, registration, or app download required
  • Mobile-friendly and works on phones, tablets, laptops

100% Free & No Sign-Up Needed

Use all features unlimited times for free – ideal for engagement rings, wedding bands, fashion rings, or gifts.

Perfect for everyone: first-time ring buyers, couples, or international shoppers needing accurate size conversions.

How to Use Our Ring Size Calculator

  1. Choose your preferred method: Visual Sizer, Diameter, Circumference, Converter, or Quick Finder.
  2. Visual Sizer: Adjust the slider to match your ring or finger size visually.
  3. Diameter Method: Measure the inside diameter of a well-fitting ring and enter the value.
  4. Circumference Method: Wrap string/paper around your finger, measure the length, and enter circumference.
  5. Converter: Select your known size system, enter the size value, and see all equivalent sizes.
  6. Quick Finder: Select finger type and ring style for personalized size recommendations.
  7. View your size instantly in all 5 international formats (India, US, UK, EU, JP).
  8. Download the printable PDF sizer for ultimate accuracy with 50mm calibration line.

Releted Ring Size Calculator Tools

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Got Questions? We have you covered

With multiple measurement methods available, accuracy is high when used correctly. The Visual Sizer provides good estimates, while the Diameter and Circumference methods offer precision comparable to professional measurements. For best results, use the printable PDF version or confirm with a jeweler.
We offer 5 methods: 1) Visual Sizer - interactive slider to match ring visually, 2) Diameter Method - measure inside diameter of existing ring, 3) Circumference Method - measure around finger or ring, 4) International Converter - convert between size systems, 5) Quick Finder - personalized recommendations.
Absolutely! We support 5 international sizing systems including India (IN), US, UK, EU, and JP. All sizes are displayed simultaneously for easy comparison.
Yes! Use the Circumference Method to measure your finger directly with string or paper, or use the Quick Finder for personalized recommendations based on finger type and ring style.
Yes, printing at 100% scale with the 50mm check line provides jeweler-level precision. It's the most accurate method for measuring at home.
No – completely free, no registration, no app needed. Everything works directly in your browser with no credit card or account required.
Fingers swell slightly during the day due to temperature and activity. Measure in the evening when fingers are largest for the most comfortable fit throughout the day.
Use our International Size Converter: select your known size system (IN, US, UK, EU, or JP), enter your size value, and instantly see the equivalent sizes in all other systems.

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O-Ring Diameter Calculator - Toolsnak