Tire Section Width Calculator
Work back to the width from the other sizes. Use the calculator below. Results update as you type.
Section Width = Sidewall Height / (Aspect Ratio / 100)How the Tire Section Width Calculator Works
This calculator works by dividing a known sidewall height by the aspect ratio expressed as a decimal. It solves the width when the sidewall height and profile are known but the size code is not.
- Enter the measured or target sidewall height, for example 110 mm (4.33 in).
- Enter the aspect ratio, for example 50.
- Read the section width: 220 mm (8.66 in).
- Round the result to the nearest real width step, here 215 mm or 225 mm.
The tool helps when you have a worn or unmarked tire, or a target profile from a spec sheet.
The Formula
The formula is Section Width = Sidewall Height ÷ (Aspect Ratio ÷ 100). It is the sidewall formula rearranged to solve for width.
Section Width (mm) = Sidewall Height (mm) ÷ (Aspect Ratio ÷ 100) Section Width (in) = Section Width (mm) ÷ 25.4Worked example: a sidewall of 120 mm at a 60 aspect ratio gives 120 ÷ 0.60 = 200 mm (7.87 in). A 120 mm sidewall at a 45 aspect ratio needs a 266.7 mm width, which rounds to 265 mm.
Passenger and light truck widths are sold in 10 mm steps ending in 5 (195, 205, 215). Round to that pattern before searching for tires.
Conversion Table
The conversion table solves the section width for 6 sidewall heights and 7 aspect ratios. Each cell is a width in millimeters.
Read across a sidewall row: a 100 mm (3.94 in) sidewall needs a 250 mm width at 40%, a 200 mm width at 50% and a 143 mm width at 70%. The note under the table explains rounding to the nearest sold width.
| Sidewall (mm / in) | 40% | 45% | 50% | 55% | 60% | 65% | 70% |
|---|---|---|---|---|---|---|---|
| 80 / 3.15 | 200 | 178 | 160 | 145 | 133 | 123 | 114 |
| 90 / 3.54 | 225 | 200 | 180 | 164 | 150 | 138 | 129 |
| 100 / 3.94 | 250 | 222 | 200 | 182 | 167 | 154 | 143 |
| 110 / 4.33 | 275 | 244 | 220 | 200 | 183 | 169 | 157 |
| 120 / 4.72 | 300 | 267 | 240 | 218 | 200 | 185 | 171 |
| 140 / 5.51 | 350 | 311 | 280 | 255 | 233 | 215 | 200 |
Round the solved width to the nearest 5 mm step used on real tire sizes (215, 220, 225, and so on).
What Is the Tire Section Width Calculator?
The Tire Section Width Calculator is a reverse tool that finds the tire width needed to produce a chosen sidewall height at a chosen aspect ratio. Section width is the widest distance across an inflated tire, excluding raised letters and rim guards.
Section width sets the size of the contact patch, the clearance to suspension parts and the approved rim width range. Width is measured on a specific measuring rim; mounting the tire on a wider or narrower rim changes the width by about 5 mm (0.2 in) per 0.5 in (12.7 mm) of rim width.
Common Uses
This calculator has 4 uses: identifying unmarked tires, solving target profiles, checking strut clearance and choosing rim widths.
- Identify unmarked tires: Work backward from a measured sidewall and a known profile.
- Solve target profiles: Find the width that gives a desired sidewall height.
- Check strut clearance: Compare the solved width with the space inside the wheel well.
- Choose rim widths: Use the width to look up the approved rim range.