Free Tire Size Calculator
Calculate the overall diameter, circumference, and sidewall height from a metric tire size.
mm
%
in
Overall Diameter
26.7 in
Circumference84.0 in
Sidewall Height4.87 in
Revolutions Per Mile754
Overall Diameter vs Tire Width
How to Read a Tire Size
A tire marked 225/55R17 means: 225 mm width, 55% aspect ratio (sidewall height as % of width), R = radial, 17-inch rim.
Formula
Sidewall = Width x Aspect Ratio / 100 (in mm)
Overall Diameter = Rim Diameter + 2 x Sidewall (converted to inches)
Circumference = Diameter x pi
Example Calculation
Tire size 225/55R17.
- 01Sidewall = 225 x 55/100 = 123.75 mm = 4.87 in
- 02Overall diameter = 17 + 2 x 4.87 = 26.74 in
- 03Circumference = 26.74 x 3.1416 = 84.0 in
- 04Revolutions per mile = 63,360 / 84.0 = 754
Frequently Asked Questions
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