Tire Size Calculator

Results use standard ISO/ETRTO formulas from the size code you enter. They reflect nominal published dimensions for a new tire at rated pressure and are reliable for comparing sizes. Mounted tires can differ by model, tread depth, pressure, and load.

• Sidewall height = section width × aspect ratio
• Overall diameter = wheel diameter + two sidewalls
• Circumference = π × overall diameter
• Revolutions per mile = inches per mile ÷ circumference

Metric sidewall uses width in millimetres and aspect ratio as a percentage. Results are nominal values from the size code, not measured on a specific tire model.

Manufacturers build to nominal specs, but real mounted height and width change with tread wear, inflation, load, rim width, and construction. A tape-measured tire often reads slightly different from the label-based calculation.

No. It reports mathematical dimensions only. Wheel width, offset, load rating, speed rating, and fender or suspension clearance must be verified with the vehicle and tire manufacturer or a qualified installer.

It is the theoretical number of complete tire revolutions over one mile, based on calculated circumference. Speedometers and odometers depend on rolling distance; manufacturer or measured values may differ slightly.

Only when the wheel diameter in the size code matches—the number after the R (or in a flotation size). Overall diameter and section width can still differ. Always follow the tire maker’s approved rim width and diameter range.

A taller tire travels farther per revolution, so the speedometer may read lower than actual speed—and the opposite when diameter decreases. Error scales roughly with diameter change. Use the tire comparison calculator with your stock and new sizes for a specific estimate.

Overall diameter is the full height of the mounted tire from ground to tread crown. Radius is half of that—the distance from the wheel centerline to the tread. Tire size labels encode values used to calculate diameter, not radius directly.