Tire Size Calculator & Comparison
Compare two tire sizes side-by-side. See diameter, width, speedometer difference and more.
How It Works
Enter two tire sizes in either metric (e.g. P265/70R17, LT285/75R16) or flotation (e.g. 33x12.50R15) format.
The calculator converts each size to inches, computes overall diameter, section width, sidewall height, circumference, and revolutions per mile, then displays a side-by-side comparison with color-coded differences.
Speedometer error is calculated by comparing the circumference of both tires. A larger replacement tire means your speedometer will read lower than your actual speed.
How to Read a Tire Size
A tire size like P265/70R17 breaks down as:
- P — Passenger tire (LT = Light Truck)
- 265 — Section width in millimeters
- 70 — Aspect ratio (sidewall height is 70% of width)
- R — Radial construction
- 17 — Rim diameter in inches
Flotation sizes like 33x12.50R15 use inches: 33" overall diameter × 12.5" width on a 15" rim.
Frequently Asked Questions
How much bigger can I go without a lift?
Most trucks and SUVs can safely fit tires about 1 inch larger in overall diameter without any suspension modifications. Going beyond that often requires a leveling kit or lift, plus possible fender trimming to avoid rubbing at full steering lock.
Will different tire sizes affect my gas mileage?
Yes. Larger tires are heavier and have more rolling resistance, which typically reduces fuel economy by 1–3 mpg. Wider tires also increase aerodynamic drag. The effect is larger if the tires are significantly heavier than stock.
Can I compare metric and flotation tire sizes?
Absolutely. Enter a metric size like 265/70R17 in one field and a flotation size like 33x12.50R15 in the other. The calculator converts both to the same units for an accurate side-by-side comparison.
What does 'revolutions per mile' tell me?
Revolutions per mile indicates how many times the tire rotates in one mile. A larger tire has fewer revolutions per mile. This value is used to calculate speedometer error—if the new tire has different revs per mile than stock, your speedometer will read incorrectly.
Is it okay to mix two different tire sizes on the same vehicle?
Running different tire sizes on the same axle is not recommended because it causes uneven handling and can damage differentials. Some vehicles use staggered setups (wider rears) from the factory, but check your owner's manual before mixing sizes.