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Tire Diameter Calculator

Calculate overall tire diameter, circumference, and revs per mile.

Last updated: June 13, 2026

Calculator

Tire Width

Aspect Ratio

Rim Diameter

Results

Overall Diameter26.7"

679 mm

Sidewall Height4.9"

124 mm

Circumference84.0"

2.13 m

Revolutions per Mile754

How to Use This Calculator

1Enter your tire width in mm.
2Enter the aspect ratio percentage.
3Enter the rim diameter in inches.
4View diameter, sidewall height, circumference, and revolutions per mile.

Formula Explanation

Tire diameter is calculated from width, aspect ratio, and rim diameter using standard tire sizing conventions.

Diameter = (Width × Aspect Ratio / 100 × 2 + Rim × 25.4) ÷ 25.4

Variables:

WidthTire width in millimeters

Aspect RatioSidewall height as percentage of width

RimWheel diameter in inches

Worked Examples

225/55R17 Tire

1. Sidewall = 225 × 0.55 = 123.75mm
2. Diameter = (123.75 × 2 + 17 × 25.4) ÷ 25.4

Result: Diameter: 26.7 inches

Why Use This Calculator

Essential for tire shopping and compatibility checks.
Shows revolutions per mile for accurate speedometer calibration.
Helps compare different tire sizes before purchasing.
Includes both imperial and metric measurements.

336 × 280 Large Rectangle

300 × 250 Medium Rectangle

Tips & Best Practices

Use this before buying new tires to ensure fitment.
Check your vehicle manual for approved tire size ranges.
Larger diameters affect speedometer accuracy and fuel economy.

Common Mistakes to Avoid

❌ Forgetting that aspect ratio is a percentage of width.

✅ A 55 aspect ratio on a 225mm tire means 123.75mm sidewall, not 55mm.

❌ Comparing only diameter without checking width.

✅ Wider tires may rub on fenders even if diameter is similar.

Frequently Asked Questions

What does 225/55R17 mean?

225 is the tire width in mm, 55 is the aspect ratio (sidewall height as % of width), R means radial construction, and 17 is the rim diameter in inches.

How does tire diameter affect my speedometer?

A larger diameter tire covers more ground per revolution, making your speedometer read lower than actual speed. Each 1% increase in diameter means your actual speed is 1% faster than displayed.

336 × 280 Large Rectangle

300 × 250 Medium Rectangle

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Height

<iframe src="https://redicalc.com/embed/automotive/tire-diameter-calculator" width="100%" height="600" style="border:none;border-radius:12px;box-shadow:0 1px 3px rgba(0,0,0,0.1);" title="Tire Diameter Calculator — RediCalc.com" loading="lazy" allowtransparency="true"></iframe>

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Disclaimer: This calculator is provided for informational and educational purposes only. Results are estimates and should not be used as a substitute for professional advice. RediCalc.com makes no guarantees regarding the accuracy, completeness, or suitability of any calculations. Always consult a qualified professional before making financial, health, construction, or other important decisions.

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