RollingSpecTire Diameter Calculator
Enter one tire size to instantly get overall diameter, width, sidewall height, circumference and approximate revolutions per mile.
Results are estimates based on nominal dimensions. Actual tire dimensions may vary by manufacturer and model.
How tire diameter is calculated
Diameter = wheel diameter + 2 × sidewall height.
Sidewall height is the tire width multiplied by the aspect ratio. Wheel diameter is given in inches and converted to millimeters for the calculation, then the result is converted back to inches for display.
Tire size example
For a 265/70R17: sidewall height = 265 × 0.70 = 185.5 mm. Diameter = (17 × 25.4) + (2 × 185.5) = 802.8 mm ≈ 31.61 inches.
Tire diameter vs wheel diameter
A "17-inch wheel" refers only to the metal wheel diameter. It does not mean the tire's overall diameter is 17 inches — the mounted tire's sidewalls add significant height on top of the wheel, so overall diameter is typically much larger than the wheel size alone.
Why overall tire diameter matters
Overall diameter affects speedometer accuracy, effective gearing, ride height, and wheel-well clearance. Comparing two sizes' overall diameter is more informative than comparing wheel size alone.
Comparing an old and new tire? Use the Tire Size Calculator.
FAQ
What is the diameter of a 265/70R17 tire?
A 265/70R17 has a sidewall height of 265 × 0.70 = 185.5 mm, giving an overall diameter of (17 × 25.4) + (2 × 185.5) ≈ 802.8 mm, or about 31.6 inches.
How do I convert tire size to inches?
Enter the width, aspect ratio and wheel diameter from the tire's size code. The calculator converts the metric width and sidewall height to inches and adds them to the wheel diameter to get overall diameter in inches.
How is tire height calculated?
Tire height (sidewall height) equals the tire's width in millimeters multiplied by its aspect ratio, expressed as a percentage. For example, 225 mm × 65% = 146.25 mm.
Is tire diameter the same as wheel diameter?
No. Wheel diameter (e.g. 17 inches) refers only to the metal wheel. Overall tire diameter includes two sidewall heights on top of the wheel diameter, so a tire mounted on a 17-inch wheel typically has an overall diameter around 28-32 inches depending on its aspect ratio and width.
Why do actual tire dimensions differ from calculated size?
These formulas use nominal dimensions from the tire size code. Actual manufactured dimensions vary slightly between brands and models, and mounted/inflated dimensions can differ further from the nominal spec.