Enter a tire size to get its overall diameter, sidewall height, circumference, and revolutions per mile. A free tire size calculator for planning plus-sizes and checking tire height before you buy.
Tire Specs
Tire Diagram
Scaled front view — overall diameter, the wheel (dashed), and section width.
How tire sizes work
A tire size like 245/40R18 means a 245 mm section width, a sidewall that is 40% of that width, mounted on an 18 inch wheel. Overall diameter drives your speedometer reading, ride height, and clearance — keep a new size within about 3% of stock for accuracy.
Use this tire size calculator to plan a plus-size or check tire height. Pair it with our tire size comparison and wheel fitment calculator, then shop tires and wheels that fit your build.