Tyre Circumference
Calculator
Results
- Tyre outside diameter (mm)
- 634.3
- Tyre circumference (m)
- 1.992712
- Tyre revolutions per km
- 501.828608
- Sidewall height (mm)
- 101.25
Results
| Tyre outside diameter (mm) | 634.3 |
| Tyre circumference (m) | 1.992712 |
| Tyre revolutions per km | 501.828608 |
| Sidewall height (mm) | 101.25 |
formula-map diagram
- Tyre outside diameter (mm)
- 634.3
- Tyre circumference (m)
- 1.992712
- Tyre revolutions per km
- 501.828608
- Sidewall height (mm)
- 101.25
Formula breakdown
Formula
d = rim × 25.4 + 2 × width × aspect ÷ 100; C = π × d= 634.3
Note
Simplified model: results use idealised textbook relationships and ignore real-world factors such as driving style, load, temperature, aerodynamic and rolling losses, drivetrain efficiency, tyre and brake condition and road surface. CO2 figures are tailpipe only, based on the standard 2.31 kg CO2 per litre of petrol (2.68 kg per litre of diesel), and exclude fuel production and distribution. Use them as estimates, not as legal, safety or load-rating figures.
More in Automotive and transport
See all →Frequently asked questions
What is tyre circumference and why is it needed for speed and odometer calculations?+
Tyre circumference is the total distance the tire covers in one complete revolution. It's the key figure that links wheel rotation (RPM) to actual road distance and speed, which is why speedometers, odometers, and gear ratio calculations all depend on an accurate circumference figure.
How is tyre circumference calculated from the tire size code (e.g., 225/45R17)?+
The sidewall height is calculated from the width and aspect ratio (225mm × 45% = 101.25mm), doubled for both sidewalls and added to the wheel diameter (17 inches converted to mm) to get overall tire diameter, then circumference = π × diameter.
Why does the aspect ratio (the middle number in a tire size) matter so much for circumference?+
The aspect ratio determines sidewall height as a percentage of tire width, and sidewall height directly affects overall tire diameter. A lower-profile tire (smaller aspect ratio) on the same width and wheel diameter has less sidewall and therefore a smaller overall diameter and circumference than a higher-profile tire.
What's a common misconception about changing tire size and keeping the 'same' overall diameter?+
People sometimes assume any tire that 'looks about the same size' will preserve speedometer accuracy and gearing, but even a 2-3% difference in overall diameter (a common tolerance target) is measurable, and larger swings when going to a different wheel diameter can meaningfully change effective gearing and speedometer accuracy.
How does this calculation affect actual road speed versus indicated speed?+
If actual tire circumference is larger than what the vehicle's speedometer was calibrated for, actual speed will be higher than indicated, since the vehicle covers more distance per wheel rotation than the speedometer assumes. Smaller-than-stock tires have the opposite effect, making indicated speed higher than actual speed.