Tire Size Calculator
Original Tire
New Tire
Common Tire Size Diameters
Overall diameter in inches for popular tire sizes
| Tire Size | Diameter | Circumference | Rev/Mile |
|---|---|---|---|
| 205/55R16 | 24.9" | 78.1" | 811 |
| 215/60R16 | 26.2" | 82.1" | 772 |
| 225/60R16 | 26.6" | 83.6" | 758 |
| 225/45R17 | 25.0" | 78.5" | 807 |
| 245/45R17 | 25.7" | 80.6" | 786 |
| 255/55R18 | 28.0" | 88.0" | 720 |
| 265/70R17 | 31.6" | 99.3" | 638 |
| 275/60R20 | 33.0" | 103.5" | 612 |
| 315/70R17 | 34.4" | 108.0" | 587 |
How We Calculate This
This tire size calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
How to Convert Oven Recipes to Air Fryer
Tire diameter is calculated from the metric tire size format (e.g. 225/60R16) using the section width, aspect ratio, and rim diameter.
The basic rule:
- Sidewall height = section width (mm) × aspect ratio / 100
- Overall diameter = (2 × sidewall height / 25.4) + rim diameter in inches
- Circumference = π × diameter
- Revolutions per mile = 63,360 ÷ circumference in inches
- Speedometer error = ((new diameter − original diameter) / original diameter) × 100%
Most manufacturers recommend staying within 3% of the original tire diameter. Larger tires make your speedometer read slower than actual speed.
When Would You Use This Calculator?
This tire size calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
How do I read a tire size like 225/60R16?
225 is the section width in millimeters, 60 is the aspect ratio (sidewall height is 60% of width), R means radial construction, and 16 is the rim diameter in inches.
How does tire size affect the speedometer?
A larger tire covers more ground per revolution, so your speedometer will read lower than your actual speed. A 3% larger tire means at an indicated 60 mph, you're actually going about 61.8 mph.
What is the 3% rule for tire sizes?
Most vehicle manufacturers recommend staying within 3% of the original tire diameter. Going beyond this can affect speedometer accuracy, ABS, traction control, and may cause rubbing on fenders or suspension components.
Does tire size affect fuel economy?
Yes. Larger tires are heavier and have more rolling resistance, which can decrease fuel economy by 1-2 MPG. Wider tires also increase aerodynamic drag slightly. However, the effect is usually small within the 3% range.