Tire Sidewall Height Calculator
Find the sidewall from the width and the aspect ratio. Use the calculator below. Results update as you type.
Sidewall Height = Width × (Aspect Ratio / 100)How the Tire Sidewall Height Calculator Works
This calculator works by multiplying the section width by the aspect ratio percentage. The answer is the height of the rubber between the rim edge and the tread surface.
- Enter the section width in mm, for example 245.
- Enter the aspect ratio, for example 40.
- Read the sidewall height: 98.0 mm (3.86 in).
The rim diameter does not change sidewall height. A 245/40R18 and a 245/40R20 have the same 98 mm sidewall; only the wheel inside it changes.
The Formula
The formula is Sidewall Height = Width × (Aspect Ratio ÷ 100). The answer is in millimeters; divide by 25.4 for inches.
Sidewall Height (mm) = Width (mm) × Aspect Ratio ÷ 100 Sidewall Height (in) = Sidewall Height (mm) ÷ 25.4Worked example for 275/65R18: 275 × 0.65 = 178.75 mm, and 178.75 ÷ 25.4 = 7.04 in.
The aspect ratio is a percentage, not a fixed height. A 45 series tire has a sidewall 45% as tall as it is wide, so a wider 45 series tire has a taller sidewall than a narrower one.
Conversion Table
The conversion table gives sidewall height for 6 widths and 5 aspect ratios, in millimeters with inches in brackets. Widths run from 195 mm to 295 mm and aspect ratios from 35 to 75.
Find your width in the left column and move across to your aspect ratio. A 235 mm tire at 55% has a 129.3 mm (5.09 in) sidewall. Moving down one row (20 mm wider) at the same aspect ratio adds 7–15 mm of sidewall.
| Width \ Aspect | 35 series | 45 series | 55 series | 65 series | 75 series |
|---|---|---|---|---|---|
| 195 mm | 68.2 (2.69) | 87.8 (3.45) | 107.2 (4.22) | 126.8 (4.99) | 146.2 (5.76) |
| 215 mm | 75.2 (2.96) | 96.8 (3.81) | 118.2 (4.66) | 139.8 (5.50) | 161.2 (6.35) |
| 235 mm | 82.2 (3.24) | 105.8 (4.16) | 129.2 (5.09) | 152.8 (6.01) | 176.2 (6.94) |
| 255 mm | 89.2 (3.51) | 114.8 (4.52) | 140.2 (5.52) | 165.8 (6.53) | 191.2 (7.53) |
| 275 mm | 96.2 (3.79) | 123.8 (4.87) | 151.2 (5.95) | 178.8 (7.04) | 206.2 (8.12) |
| 295 mm | 103.2 (4.06) | 132.8 (5.23) | 162.2 (6.39) | 191.8 (7.55) | 221.2 (8.71) |
What Is the Tire Sidewall Height Calculator?
The Tire Sidewall Height Calculator is a tool that converts width and aspect ratio into the physical height of a tire's sidewall. Other names for sidewall height are section height and profile height.
Sidewall height affects 4 driving traits: ride comfort, steering response, rim protection and off-road flex. Tall sidewalls (above 5 in or 127 mm) absorb potholes and air down well. Short sidewalls (under 4 in or 102 mm) give quicker steering and expose the rim to curb damage.
Two sidewalls plus the rim make up overall diameter, so this number is the first step in every tire size calculation.
Common Uses
This calculator has 5 uses: ride-comfort planning, plus-size checks, off-road setup, rim-protection checks and profile matching.
- Plan ride comfort: Compare the cushion height of two candidate sizes.
- Check plus sizes: See how much sidewall a larger wheel removes.
- Set up off-road tires: Pick a sidewall tall enough for low-pressure trail use.
- Protect rims: Avoid sidewalls under 3.5 in (89 mm) on rough roads.
- Match profiles: Keep the same visual profile across front and rear axles.