Tire Size Calculator

What does 225/45R17 mean?

225/45R17 describes a nominal 225 mm width, a sidewall equal to 45% of that width, radial construction and a 17-inch rim. Those numbers describe size, not approved rim-width range, load capacity or actual mounted measurements.

The first number is nominal section width in millimetres. The middle number is sidewall height as a percentage of that width, not a height in millimetres. The last number is wheel diameter in inches. R indicates radial construction; load index and speed rating are separate markings not decoded here.

Enter a complete size such as 225/45R17. Spaces and hyphens are accepted variants. A partly entered size does not produce results. The geometric values are calculated from the size designation, not a database of manufacturer measurements.

Sidewall height and overall diameter

Sidewall height = width × aspect ratio ÷ 100. Overall diameter = rim diameter × 25.4 + two sidewall heights. Increasing rim diameter alone therefore increases overall diameter; reducing the profile can offset that change.

The profile illustration scales the rim and tire from those calculated dimensions. It helps distinguish the metal rim from the two sidewalls, but does not model a real tire's tread, shoulder, bead or deflection.

Circumference and revolutions

Nominal circumference = π × diameter. Revolutions per kilometer = 1,000,000 ÷ circumference in millimetres; revolutions per mile = 1,609,344 ÷ that same circumference. Both outputs are available here because changing distance units does not create a different calculation task.

Geometric circumference is not loaded rolling circumference. Tire pressure, load, construction, wear and the manufacturer's measuring procedure change measured revolutions. Use manufacturer rolling data when accuracy for a specific tire matters.

Choose the next task, not another duplicate calculator

Use Tire Size Comparison to compare two specifications, Speedometer Error for an indicated-to-actual estimate, and the Converter for metric/flotation notation. Diameter, sidewall, circumference and revolutions are all outputs of this central tool, not separate near-identical pages.

A width or diameter match does not demonstrate approved rim compatibility, clearance, load capacity or vehicle suitability. Consult the vehicle placard and the tire manufacturer's specifications.

Example: dimensions of 225/45R17

Inputs: Tire size: 225/45R17. Metric results below are computed by the same engine as the live tool.

225/45R17 has a nominal diameter of 634.3 mm and a sidewall height of 101.3 mm. Both distance-unit revolution counts are calculated from the same circumference.

Important limitations