Tire Aspect Ratio Calculator
Find the aspect ratio from the sidewall and the width. Use the calculator below. Results update as you type.
Aspect Ratio = (Sidewall Height / Section Width) × 100How the Tire Aspect Ratio Calculator Works
This calculator works by dividing sidewall height by section width and multiplying by 100. The answer is the profile number printed after the slash in a size code.
- Enter the sidewall height in inches or mm, for example 4.0 in (101.6 mm).
- Enter the section width, for example 225 mm.
- Read the aspect ratio: 45.2%.
- Round to the nearest 5 to find the sold size, here the 45 series.
Use the tool with a tape measure on an unmarked tire or with figures from a spec sheet.
The Formula
The formula is Aspect Ratio = (Sidewall Height ÷ Section Width) × 100. Both values must use the same unit before dividing.
Aspect Ratio (%) = (Sidewall Height (mm) ÷ Section Width (mm)) × 100 Sidewall Height (mm) = Sidewall Height (in) × 25.4Worked example: a 5.0 in sidewall is 127 mm. On a 245 mm tire, 127 ÷ 245 × 100 = 51.8%. The nearest sold profile is 50, giving 245/50.
Aspect ratios sold today run from 20 (ultra-low-profile performance tires) to 85 (light truck and trailer tires).
Conversion Table
The conversion table solves the aspect ratio for 7 sidewall heights and 5 widths. Sidewalls run from 3.0 in (76.2 mm) to 7.0 in (177.8 mm); widths run from 205 mm to 285 mm.
Find your sidewall height in the first column and read across to your width. A 6.0 in sidewall on a 265 mm tire gives 57.5%, which sits between the 55 and 60 series.
| Sidewall (in / mm) | 205 mm | 225 mm | 245 mm | 265 mm | 285 mm |
|---|---|---|---|---|---|
| 3.0 / 76.2 | 37.2 | 33.9 | 31.1 | 28.8 | 26.7 |
| 3.5 / 88.9 | 43.4 | 39.5 | 36.3 | 33.5 | 31.2 |
| 4.0 / 101.6 | 49.6 | 45.2 | 41.5 | 38.3 | 35.6 |
| 4.5 / 114.3 | 55.8 | 50.8 | 46.7 | 43.1 | 40.1 |
| 5.0 / 127.0 | 62.0 | 56.4 | 51.8 | 47.9 | 44.6 |
| 6.0 / 152.4 | 74.3 | 67.7 | 62.2 | 57.5 | 53.5 |
| 7.0 / 177.8 | 86.7 | 79.0 | 72.6 | 67.1 | 62.4 |
Real tires use aspect ratios in steps of 5, so 44.8 rounds to the 45 series.
What Is the Tire Aspect Ratio Calculator?
The Tire Aspect Ratio Calculator is a tool that converts a sidewall height and a section width into the profile percentage used in tire size codes. Other names for aspect ratio are series and profile.
The number describes shape, not size. A 70 series tire has a sidewall 70% as tall as its width, and a 35 series tire has a sidewall 35% as tall. Low numbers mean a short, stiff sidewall; high numbers mean a tall, soft sidewall.
Inch-based flotation sizes such as 33x12.50R15 do not print an aspect ratio. The calculator finds one: (33 − 15) ÷ 2 = 9.0 in of sidewall on a 12.5 in width gives 72%.
Common Uses
This calculator has 4 uses: decoding unmarked tires, converting flotation sizes, matching profiles and setting plus-size targets.
- Decode unmarked tires: Turn tape measurements into a size code.
- Convert flotation sizes: Find the implied profile of inch-marked truck tires.
- Match profiles: Keep the same series across axles or trims.
- Set plus-size targets: Find the profile that holds diameter on a larger wheel.