About the Tire Size Converter
What is the Tire Size Converter?
A tyre marked 195/55 R16 has a 195 mm width, a sidewall 55% of that width and a 16-inch rim. This tire size converter turns those numbers into real dimensions.
Compare your current and new sizes to check fit and speedometer accuracy.
How to use the Tire Size Converter
- Current Tyre – Width (mm) (sample: 195)
- Current Tyre – Aspect Ratio (%) (sample: 55)
- Current Tyre – Rim (inches) (sample: 16)
- New Tyre – Width (mm) (sample: 205)
- New Tyre – Aspect Ratio (%) (sample: 55)
- New Tyre – Rim (inches) (sample: 16)
- Press Compare Tyre Sizes (results also refresh as you type). The result card shows the Diameter Difference, along with Current tyre diameter, New tyre diameter, Current sidewall height and New sidewall height.
Formula used
Diameter = Rim × 25.4 + 2 × Width × Aspect ÷ 100
- Width = section width in mm
- Aspect = sidewall height as % of width
- Rim = rim diameter in inches
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Current Tyre – Width (mm) | 195 |
| Current Tyre – Aspect Ratio (%) | 55 |
| Current Tyre – Rim (inches) | 16 |
| New Tyre – Width (mm) | 205 |
| New Tyre – Aspect Ratio (%) | 55 |
| New Tyre – Rim (inches) | 16 |
| Result | Value |
|---|---|
| Diameter Difference | 1.77% |
| Current tyre diameter | 620.9 mm |
| New tyre diameter | 631.9 mm |
| Current sidewall height | 107.3 mm |
| New sidewall height | 112.8 mm |
| Actual speed when the speedometer shows 60 km/h | 61.1 km/h |
| Revolutions per km (new tyre) | 504 |
| Verdict | Within ±3% – generally acceptable |
Tips for using the Tire Size Converter
- Keep the overall diameter within ±3% of the original.
- A larger diameter makes the speedometer read low – you travel faster than shown.