Tire Size Calculator
Enter a tire size code (e.g., 225/55R17) to see overall diameter, width, sidewall height, circumference, and revolutions per mile in both inches and millimeters.
Tire Dimensions — 225/55R17
26.74 inches
Diameter
679.3 mm
Section Width
8.86″ / 225mm
Sidewall
4.87″ / 123.8mm
Revs/Mile
754
💡 Circumference: 84.02″ (2134.1 mm)
💡 How to Use the Tire Size Calculator
How to Read a Tire Size Code
A tire marked 225/55R17 contains three critical measurements:
- 225 — Tread width in millimeters (the contact patch width)
- 55 — Aspect ratio (sidewall height = 55% of the tread width)
- R17 — Radial construction, fits a 17-inch rim
Calculating Tire Dimensions
| Dimension | Formula | Example (225/55R17) |
|---|---|---|
| Sidewall Height | Width × (Aspect ÷ 100) | 225 × 0.55 = 123.75mm (4.87") |
| Overall Diameter | Rim + 2 × Sidewall | 17" + 2 × 4.87" = 26.74" |
| Circumference | π × Diameter | 3.14159 × 26.74" = 84.0" |
| Revolutions/Mile | 63,360 ÷ Circumference | 63,360 ÷ 84.0 = 754 rev/mile |
Other Tire Coding Systems
P-Metric: P225/55R17 — "P" means passenger car. This is the most common US format.
LT-Metric: LT265/70R17 — "LT" means Light Truck, built for heavier loads and trailer towing.
Flotation: 33×12.50R15 — Used for off-road tires. 33 = diameter in inches, 12.50 = width in inches, R15 = 15-inch rim. Common on Jeeps, Broncos, and lifted trucks.
Tire Load & Speed Ratings
After the tire size, you'll see additional codes like 99V:
- 99 — Load index (1,709 lbs per tire max)
- V — Speed rating (149 mph max sustained speed)
| Speed Rating | Max Speed |
|---|---|
| S | 112 mph (180 km/h) |
| T | 118 mph (190 km/h) |
| H | 130 mph (210 km/h) |
| V | 149 mph (240 km/h) |
| W | 168 mph (270 km/h) |
| Y | 186 mph (300 km/h) |