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Tire Height Calculator

Calculate tire diameter from metric sizes (e.g., 205/55R16).

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Inputs

in

Your values stay on this device.

Results

Total Diameter
Sidewall Height4.44
Circumference78.16

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Assumptions

  • The tire size follows the standard metric format width/aspect-rim.
  • The result is approximate and should be checked against the vehicle placard.
  • Clearance, suspension, and load ratings are not modeled here.

Sensitivity preview

Width (mm) -10%: Total Diameter 23.99 in

Width (mm) Current: Total Diameter 24.88 in

Width (mm) +10%: Total Diameter 25.77 in

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About this Tire Size Calculator

Reading a tire sidewall can be confusing. The numbers (e.g., 205/55R16) mix metric (width in mm) and percentages (aspect ratio). This calculator decodes those numbers into the actual height and width of the tire in inches.

Who this calculator is for

  • Drivers comparing replacement tire sizes.
  • Shoppers checking whether a tire will fit a specific wheel.
  • People estimating speedometer changes after a tire upgrade.

When to use it

  • Convert a metric tire code into inches.
  • Compare a factory tire to a possible replacement size.
  • Estimate sidewall height, total diameter, and circumference.

How to use this calculator

  1. Enter the Width (First number, e.g., 205).
  2. Enter the Aspect Ratio (Second number, e.g., 55).
  3. Enter the Rim Diameter (Third number, e.g., 16).
  4. The result shows the Total Diameter and Sidewall Height.

Key assumptions

  • The tire size follows the standard metric format width/aspect-rim.
  • The result is approximate and should be checked against the vehicle placard.
  • Clearance, suspension, and load ratings are not modeled here.

Accuracy and testing

Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.

View accuracy page

How this calculator works

1. Sidewall Height (mm) = Width × (Ratio/100). 2. Sidewall (in) = Sidewall (mm) / 25.4. 3. Total Diameter = Rim + (2 × Sidewall).

Inputs explained

Width (mm)

The width of the tire tread in millimeters.

Aspect Ratio

The height of the sidewall as a percentage of the width. A lower number means a 'low profile' tire.

Rim Diameter

The size of the wheel the tire mounts on, in inches.

Understanding your results

Changing tire size affects your speedometer. A taller tire (larger diameter) makes your speedometer read slower than you are actually going.

Example scenarios

Compact Car

205/55R16. Diameter: ~24.9 inches.

Truck

265/70R17. Diameter: ~31.6 inches.

Key Features

  • Metric to Inch Conversion
  • Circumference Calculation
  • Sidewall Height Logic

Tips & Best Practices

  • Keep total diameter within 3% of factory spec to avoid speedometer issues and brake failure warnings.
  • Larger tires may rub against the wheel well if the vehicle is not lifted.

Glossary of Terms

Sidewall
The vertical part of the tire between the rim and the tread.
Diameter
The total height of the tire from ground to top.

Frequently Asked Questions

What does the 'R' mean?
R stands for Radial construction, which is the industry standard for modern passenger tires. It refers to how the internal cords are laid out.
How do I know if a tire fits my car?
Check the placard inside your driver's door jamb. It lists the factory size. You can usually go slightly wider or taller, but check clearance.
Does tire size affect gas mileage?
Yes. Larger, heavier tires increase rolling resistance and weight, typically reducing fuel economy. Smaller tires may improve city mileage but increase highway RPMs.