How to use this calculator
Replace the example values with your own measurements or specifications. Keep the units shown beside each label. Results update as you type; reset restores the example.
These are nominal unloaded dimensions. Actual dimensions and rolling circumference depend on the tire model, load, pressure, and wear. This tool does not confirm vehicle fitment, load rating, speed rating, clearance, or wheel compatibility.
The formula
A worked example
For a 225/45R17 tire, sidewall height is 101.25 mm and nominal diameter is 24.97 inches. The R denotes radial construction and does not enter the geometry formula.
Common questions
Does a matching diameter prove a tire will fit?
No. Check approved sizes, wheel width, load and speed ratings, and clearance with the vehicle and tire manufacturers.
Why do manufacturer revolutions per mile differ?
Published rolling measurements reflect tire construction and loaded operation; this calculation uses a geometric circle.
Sources & calculation method
Related guidance: NHTSA TireWise: tire sizes and safety. Accessed September 9, 2026. The equation above describes this tool’s model; the reference provides practical context and does not endorse this site.
Prepared with AI assistance. Formula examples and input validation have automated checks. This page has not received an independent automotive professional review. Read our review standards.