Tire Size Calculator
Compare your current tire size with a new one. See the difference in height, width and sidewall, what your speedometer will read, and how much the ride height changes.
Comparison
| Current | New | Change |
|---|
Tire size chart
Overall diameter in inches for common passenger and light truck sizes, worked out from the size on the sidewall. Real tires vary slightly by brand and tread depth.
15 inch wheels
| Width \ ratio | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 |
|---|---|---|---|---|---|---|---|---|
| 205 | 20.6 | 21.5 | 22.3 | 23.1 | 23.9 | 24.7 | 25.5 | 26.3 |
| 215 | 20.9 | 21.8 | 22.6 | 23.5 | 24.3 | 25.2 | 26.0 | 26.9 |
| 225 | 21.2 | 22.1 | 23.0 | 23.9 | 24.7 | 25.6 | 26.5 | 27.4 |
| 235 | 21.5 | 22.4 | 23.3 | 24.3 | 25.2 | 26.1 | 27.0 | 28.0 |
| 245 | 21.8 | 22.7 | 23.7 | 24.6 | 25.6 | 26.6 | 27.5 | 28.5 |
| 255 | 22.0 | 23.0 | 24.0 | 25.0 | 26.0 | 27.0 | 28.1 | 29.1 |
| 265 | 22.3 | 23.3 | 24.4 | 25.4 | 26.5 | 27.5 | 28.6 | 29.6 |
| 275 | 22.6 | 23.7 | 24.7 | 25.8 | 26.9 | 28.0 | 29.1 | 30.2 |
| 285 | 22.9 | 24.0 | 25.1 | 26.2 | 27.3 | 28.5 | 29.6 | 30.7 |
16 inch wheels
| Width \ ratio | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 |
|---|---|---|---|---|---|---|---|---|
| 205 | 21.6 | 22.5 | 23.3 | 24.1 | 24.9 | 25.7 | 26.5 | 27.3 |
| 215 | 21.9 | 22.8 | 23.6 | 24.5 | 25.3 | 26.2 | 27.0 | 27.9 |
| 225 | 22.2 | 23.1 | 24.0 | 24.9 | 25.7 | 26.6 | 27.5 | 28.4 |
| 235 | 22.5 | 23.4 | 24.3 | 25.3 | 26.2 | 27.1 | 28.0 | 29.0 |
| 245 | 22.8 | 23.7 | 24.7 | 25.6 | 26.6 | 27.6 | 28.5 | 29.5 |
| 255 | 23.0 | 24.0 | 25.0 | 26.0 | 27.0 | 28.0 | 29.1 | 30.1 |
| 265 | 23.3 | 24.3 | 25.4 | 26.4 | 27.5 | 28.5 | 29.6 | 30.6 |
| 275 | 23.6 | 24.7 | 25.7 | 26.8 | 27.9 | 29.0 | 30.1 | 31.2 |
| 285 | 23.9 | 25.0 | 26.1 | 27.2 | 28.3 | 29.5 | 30.6 | 31.7 |
17 inch wheels
| Width \ ratio | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 |
|---|---|---|---|---|---|---|---|---|
| 205 | 22.6 | 23.5 | 24.3 | 25.1 | 25.9 | 26.7 | 27.5 | 28.3 |
| 215 | 22.9 | 23.8 | 24.6 | 25.5 | 26.3 | 27.2 | 28.0 | 28.9 |
| 225 | 23.2 | 24.1 | 25.0 | 25.9 | 26.7 | 27.6 | 28.5 | 29.4 |
| 235 | 23.5 | 24.4 | 25.3 | 26.3 | 27.2 | 28.1 | 29.0 | 30.0 |
| 245 | 23.8 | 24.7 | 25.7 | 26.6 | 27.6 | 28.6 | 29.5 | 30.5 |
| 255 | 24.0 | 25.0 | 26.0 | 27.0 | 28.0 | 29.0 | 30.1 | 31.1 |
| 265 | 24.3 | 25.3 | 26.4 | 27.4 | 28.5 | 29.5 | 30.6 | 31.6 |
| 275 | 24.6 | 25.7 | 26.7 | 27.8 | 28.9 | 30.0 | 31.1 | 32.2 |
| 285 | 24.9 | 26.0 | 27.1 | 28.2 | 29.3 | 30.5 | 31.6 | 32.7 |
18 inch wheels
| Width \ ratio | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 |
|---|---|---|---|---|---|---|---|---|
| 205 | 23.6 | 24.5 | 25.3 | 26.1 | 26.9 | 27.7 | 28.5 | 29.3 |
| 215 | 23.9 | 24.8 | 25.6 | 26.5 | 27.3 | 28.2 | 29.0 | 29.9 |
| 225 | 24.2 | 25.1 | 26.0 | 26.9 | 27.7 | 28.6 | 29.5 | 30.4 |
| 235 | 24.5 | 25.4 | 26.3 | 27.3 | 28.2 | 29.1 | 30.0 | 31.0 |
| 245 | 24.8 | 25.7 | 26.7 | 27.6 | 28.6 | 29.6 | 30.5 | 31.5 |
| 255 | 25.0 | 26.0 | 27.0 | 28.0 | 29.0 | 30.0 | 31.1 | 32.1 |
| 265 | 25.3 | 26.3 | 27.4 | 28.4 | 29.5 | 30.5 | 31.6 | 32.6 |
| 275 | 25.6 | 26.7 | 27.7 | 28.8 | 29.9 | 31.0 | 32.1 | 33.2 |
| 285 | 25.9 | 27.0 | 28.1 | 29.2 | 30.3 | 31.5 | 32.6 | 33.7 |
19 inch wheels
| Width \ ratio | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 |
|---|---|---|---|---|---|---|---|---|
| 205 | 24.6 | 25.5 | 26.3 | 27.1 | 27.9 | 28.7 | 29.5 | 30.3 |
| 215 | 24.9 | 25.8 | 26.6 | 27.5 | 28.3 | 29.2 | 30.0 | 30.9 |
| 225 | 25.2 | 26.1 | 27.0 | 27.9 | 28.7 | 29.6 | 30.5 | 31.4 |
| 235 | 25.5 | 26.4 | 27.3 | 28.3 | 29.2 | 30.1 | 31.0 | 32.0 |
| 245 | 25.8 | 26.7 | 27.7 | 28.6 | 29.6 | 30.6 | 31.5 | 32.5 |
| 255 | 26.0 | 27.0 | 28.0 | 29.0 | 30.0 | 31.0 | 32.1 | 33.1 |
| 265 | 26.3 | 27.3 | 28.4 | 29.4 | 30.5 | 31.5 | 32.6 | 33.6 |
| 275 | 26.6 | 27.7 | 28.7 | 29.8 | 30.9 | 32.0 | 33.1 | 34.2 |
| 285 | 26.9 | 28.0 | 29.1 | 30.2 | 31.3 | 32.5 | 33.6 | 34.7 |
20 inch wheels
| Width \ ratio | 35 | 40 | 45 | 50 | 55 | 60 | 65 | 70 |
|---|---|---|---|---|---|---|---|---|
| 205 | 25.6 | 26.5 | 27.3 | 28.1 | 28.9 | 29.7 | 30.5 | 31.3 |
| 215 | 25.9 | 26.8 | 27.6 | 28.5 | 29.3 | 30.2 | 31.0 | 31.9 |
| 225 | 26.2 | 27.1 | 28.0 | 28.9 | 29.7 | 30.6 | 31.5 | 32.4 |
| 235 | 26.5 | 27.4 | 28.3 | 29.3 | 30.2 | 31.1 | 32.0 | 33.0 |
| 245 | 26.8 | 27.7 | 28.7 | 29.6 | 30.6 | 31.6 | 32.5 | 33.5 |
| 255 | 27.0 | 28.0 | 29.0 | 30.0 | 31.0 | 32.0 | 33.1 | 34.1 |
| 265 | 27.3 | 28.3 | 29.4 | 30.4 | 31.5 | 32.5 | 33.6 | 34.6 |
| 275 | 27.6 | 28.7 | 29.7 | 30.8 | 31.9 | 33.0 | 34.1 | 35.2 |
| 285 | 27.9 | 29.0 | 30.1 | 31.2 | 32.3 | 33.5 | 34.6 | 35.7 |
How tire size is written
A size like 245/40R18 means a tire 245 mm wide, with a sidewall 40% as tall as the width, on an 18 inch wheel. The overall diameter is the wheel size plus two sidewalls:
- Sidewall = width × ratio ÷ 100. For 245/40R18 that is 98 mm.
- Diameter = wheel diameter + 2 × sidewall. For 245/40R18 that is 457.2 + 196 = 653.2 mm, or 25.7 in.
- Revolutions per mile = 1,609,344 mm ÷ circumference in mm.
Speedometer and ride height
A taller tire covers more ground per turn, so the speedometer reads low. A shorter tire makes it read high. The calculator shows your real speed at the reading you enter. Ride height moves by half the change in diameter, since only the part of the tire below the hub lifts the car.
Bigger tires on a lowered car or a lifted truck
On a lowered car, a taller or wider tire is the first thing to rub the fender lip. Check the new size against your wheel width and offset with the wheel offset calculator. On a truck, a leveling kit or lift kit is usually what makes room for bigger tires.
Tire size FAQ
How much bigger can I go without problems?
Most people keep the overall diameter within about 3% of stock. That keeps the speedometer close, and the tire is less likely to rub.
Can I put a wider tire on my current wheels?
Often one size wider, if the wheel width is in the tire maker's approved range for that size. Check the tire maker's spec sheet.
Does a bigger tire change my gearing?
Yes. A taller tire acts like a taller gear, so the car feels a little slower to accelerate and the engine turns slower at the same speed.