About Ring Size Calculator - Accurate, Free & Private

We built Ring Size Calculator because most online tools are inaccurate. Searching for ring size calculator, ring size chart, or ring size app often leads to uncalibrated sliders that ignore screen pixel density. Our tool solves this with ISO 8653:2016 calibration: place a real credit card (85.60 mm) on your screen, calculate Pixels Per Millimeter (PMM), then measure your ring's inner diameter with D = px / PMM and C = π·D.

We are a small independent team passionate about jewelry tech. Our ring size guide covers US 3.0 to 14.0, UK F to Z+3, EU 44 to 72, Japan 4 to 29 with exact circumference and diameter from ISO ground truth. No data is sent to servers — everything runs locally in your browser. That means your measurements stay private.

What Makes Us Different

• ISO Calibrated: Unlike generic online ring size calculator tools, we use credit card (85.60 mm) or 50 mm ruler calibration for true-scale measurement.
• Complete Ring Size Chart: Includes mens ring size chart (US 8-12.5 common) and reference for average ring size for women (US 6-7), plus half sizes.
• Printable Ring Size Chart: True-to-scale at 100% with 50 mm calibration bar — works offline when you need to measure ring size without screen.
• Ring Size Adjuster & O-Ring Calculator: Doubles as ring size adjuster guide (midpoint rounding UP) and o-ring size calculator / o ring size calculator for industrial O-rings using same D and C math.
• Multilingual: Available in 6 languages, human-readable full international breakdown US/UK/EU/JP.

Our Promise

Free forever, no ads injected in measurement, no registration, no ring size app download required. We want you to learn how to measure ring size at home accurately and avoid costly resizing.

Contact us at vanshrajgupta777@gmail.com for feature requests or sponsorship.