About Tire Size Math

Tire Size Math turns a tire size like 265/70R17 into numbers: overall diameter, sidewall height, circumference and revolutions per mile. It compares two sizes side by side and works out speedometer error and effective gear ratio after a change.

Every result is plain geometry from the size printed on the sidewall. The calculators don't know your vehicle, so before changing sizes check the door placard and owner's manual, and talk to a tire professional.

Questions or a number that looks wrong? Write to hello@tiresizemath.com.