How it works
Convert physical ring diameter measurements into standard US Ring Sizes for accurate jewelry shopping.
Input query strings and outputs
Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.
Input query strings
1-
?diameter=Inside Diameter (mm)Number · Optional · Default: 16.5
Outputs
1-
resultResultText · Primary output
result contains the calculator’s complete rendered result area, including its visible result cards, tables, charts, and messages.
Determine your US ring size from physical measurements
Description
The Ring Size Calculator is a quick reference for anyone shopping for jewelry online or planning a surprise gift. Ring sizes are standardized but can vary slightly between different countries. This tool focuses on the US Sizing Scale and allows you to input the inside diameter of an existing well-fitting ring (in millimeters) to find the corresponding numerical size.
Inputs
- Inside Diameter (mm): Use a digital caliper or a precise ruler to measure the distance across the inside center of the ring.
Outputs
- Estimated Size: The corresponding US standard size (including half-sizes).
Chart
- N/A: This tool provides a direct numeric sizing result.
“Good to Know”
- Measurement Precision: A difference of just 0.8mm is an entire US size. For the best fit, measure carefully or visit a professional jeweler.
- Finger Swelling: Your fingers change size throughout the day and in different temperatures. It is best to measure your finger at the end of the day when it is at its largest.
- The Formula: The US size starts around 11.6mm (Size 0) and increases by approximately 0.81mm per full size.
- Comfort Fit: Some rings have a rounded “comfort fit” interior. You may sometimes need a slightly smaller size (approx. 0.5 size down) for these styles compared to standard flat bands.
Examples
Example 1: Small Size
- Input: 15.7 mm
- Output: US Size: 5.0
Example 2: Average Male Size
- Input: 19.8 mm
- Output: US Size: 10.0
Example 3: Mid-Size
- Input: 17.3 mm
- Output: US Size: 7.0