Tire Aspect Ratio Calculator
Calculate tire aspect ratio from section width and sidewall height. Convert measured dimensions into the series number of a tire size.
Derive aspect ratio from dimensions.
Tire Aspect Ratio Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Tire Aspect Ratio Calculator Works?
The Tire Aspect Ratio Calculator works by dividing sidewall height by section width and multiplying the result by 100. The process takes 3 steps.
Enter section width
Type the width in mm, or in inches for the calculator to convert at 25.4 mm per inch.
Enter sidewall height
Type the measured or published sidewall height, or enter overall diameter and rim size for the calculator to derive the sidewall.
Read the ratio
The calculator returns the exact ratio and the nearest standard series, rounded to a multiple of 5.
Tire Aspect Ratio Calculator Formula
The Tire Aspect Ratio Calculator formula is AR = (SH ÷ W) × 100.
AR = SH ÷ W × 100SH = (OD − Rim × 25.4) ÷ 2AR = (OD − Rim × 25.4) ÷ (2 × W) × 100- AR
- Aspect ratio, the series number (%)
- SH
- Sidewall height (mm)
- W
- Section width (mm)
- OD
- Overall diameter (mm)
Worked example
A 33x12.50R17 tire is 838.2 mm tall and 317.5 mm wide. The sidewall is (838.2 − 431.8) ÷ 2 = 203.2 mm. The aspect ratio is 203.2 ÷ 317.5 × 100 = 64.0%, so the closest metric series is 65.
Tire Aspect Ratio Calculator Conversion Table
The Tire Aspect Ratio Calculator conversion table converts 9 width and sidewall pairs into an exact aspect ratio and the nearest standard series.
| Section width | Sidewall height | Exact aspect ratio | Nearest series |
|---|---|---|---|
| 205 mm | 112.75 mm (4.44 in) | 55.0% | 55 |
| 215 mm | 129 mm (5.08 in) | 60.0% | 60 |
| 225 mm | 101.25 mm (3.99 in) | 45.0% | 45 |
| 235 mm | 105.75 mm (4.16 in) | 45.0% | 45 |
| 245 mm | 98 mm (3.86 in) | 40.0% | 40 |
| 255 mm | 89.25 mm (3.51 in) | 35.0% | 35 |
| 265 mm | 185.5 mm (7.30 in) | 70.0% | 70 |
| 275 mm | 151.25 mm (5.95 in) | 55.0% | 55 |
| 285 mm | 199.5 mm (7.85 in) | 70.0% | 70 |
What is Tire Aspect Ratio Calculator?
A Tire Aspect Ratio Calculator is a tool that works backward from tire dimensions to the aspect ratio, the second number in a metric tire size. Aspect ratio expresses sidewall height as a percentage of section width.
Standard passenger aspect ratios run from 25 to 85 in steps of 5. Low numbers such as 30 and 35 mark low-profile performance tires, and high numbers such as 70 and 75 mark truck and SUV tires.
The calculator converts flotation sizes, measured tires and target diameters into a metric series number.
What are the uses of Tire Aspect Ratio Calculator?
There are 4 main uses of the Tire Aspect Ratio Calculator, including flotation conversion and target sizing.
Flotation conversion
Convert an inch-sized truck tire into its nearest metric series.
Target sizing
Find the series that delivers a required overall diameter on a set rim.
Measured tire checks
Confirm a used tire's actual profile from tape measurements.
Unlabeled tires
Identify the series of a tire with a worn or unreadable sidewall.
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