Tire Size Calculator

Use it when your task matches one of these common needs: Decode a metric tire size such as 225/60R16. Estimate tire diameter, sidewall height, circumference, and revs per mile. It works best when you already know the section width in millimeters, aspect ratio percent, and wheel diameter in inches from a metric tire size such as 225/60R16.

In plain language: Sidewall inches = width mm x aspect ratio / 100 / 25.4. Tire diameter = wheel diameter + (2 x sidewall). Circumference = pi x diameter. Revs per mile = 63,360 / circumference. The examples on the page are there so you can compare your inputs with a 225/60R16 example before copying the answer.

Width mm: The first number on a metric tire size. In 225/60R16, the tire is listed as 225 millimeters wide. Aspect ratio: The second number. It is sidewall height as a percent of width, so 60 means the sidewall is 60% of 225 mm. Wheel diameter inches: The number after R. In 225/60R16, the tire fits a 16 inch wheel.

Read the headline answer, then check the smaller lines beside it. For everyday tools, those lines usually show the distance, time, cost, units, or setting that made the answer change.

This is a size-math estimate, not a fitment approval. Tire changes can affect clearance, load rating, speedometer readings, braking, gearing, ABS, traction control, and driver-assist systems. Follow the vehicle placard, owner manual, and tire manufacturer guidance. Also check the actual tire sidewall, vehicle placard, owner manual, rim width, load index, speed rating, brake clearance, suspension clearance, and tire manufacturer guidance.

Use 225 for width, 60 for aspect ratio, and 16 for wheel diameter. The R means radial construction; this calculator uses the three numbers for size math.

Aspect ratio changes sidewall height. With the same width, a lower aspect ratio gives a shorter sidewall and usually a smaller tire diameter unless the wheel diameter increases.

Revs per mile estimates how many times the tire turns over one mile. A tire with fewer revs per mile is usually larger, which can change speedometer reading, gearing feel, and driver-assist behavior.

Yes. A larger rolling diameter can make the speedometer read lower than actual road speed, while a smaller diameter can make it read higher. The calculator helps you spot the size change, not approve it.

No. It does not check rim width, offset, fender clearance, suspension travel, brake clearance, load index, speed rating, or manufacturer rules. Use it before you check those fitment details.

Published and calculated tire diameter can differ by tire model, tread depth, inflation pressure, load, and measuring method. Treat the answer as a close planning number.

Not directly. This page is built for metric sizes such as 225/60R16. Flotation sizes already state the approximate outside diameter and need a separate comparison method.

No. Diameter is only one check. Also match the vehicle placard, load and speed ratings, approved rim width, all-wheel-drive requirements, and any tire-shop or manufacturer guidance.

No. The tire size math runs in your browser tab. Your recent answers stay only on the page while you use it, and they are not sent to a server.