Wheel Size Calculator

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Wheel Size & Tire Diameter Calculator

Calculate total wheel height, circumference, and revolutions per mile.

First number in tire size
Middle number (percentage)
Last number (rim size)

Calculated Dimensions:

Total Diameter:
–
Sidewall Height:
–
Circumference:
–
Revs per Mile:
–

Understanding Tire and Wheel Dimensions

When upgrading your vehicle's wheels or changing tire sizes, maintaining the correct overall diameter is crucial for speedometer accuracy, gear ratios, and fender clearance. This Wheel Size Calculator helps you translate the standard metric tire code into actual physical measurements.

The Tire Size Formula

Most tires use a format like 225/45 R17. Here is how that breaks down:

  • Width (225): The width of the tire tread in millimeters.
  • Aspect Ratio (45): The height of the sidewall expressed as a percentage of the width.
  • Wheel Diameter (17): The diameter of the wheel rim in inches.

How the Math Works

To find the total diameter of your wheel and tire assembly, we use the following calculation:

  1. Convert Wheel Diameter to mm: Diameter (in) × 25.4
  2. Calculate Sidewall Height: Width (mm) × (Aspect Ratio / 100)
  3. Total Diameter: (Sidewall × 2) + Wheel Diameter (mm)
  4. Circumference: Total Diameter × π (3.14159)

Real-World Example

If you have a standard sedan tire size of 205/55 R16:

  • Sidewall Height: 205mm × 0.55 = 112.75mm
  • Wheel Diameter: 16 inches = 406.4mm
  • Total Diameter: (112.75mm × 2) + 406.4mm = 631.9mm (24.88 inches)
  • Circumference: 1,985.17mm
  • Revolutions: Approximately 810 revolutions per mile.

Note: Actual tire dimensions may vary slightly by manufacturer due to tread depth and internal construction.

function calculateWheelMetrics() { var width = parseFloat(document.getElementById('tireWidth').value); var ratio = parseFloat(document.getElementById('aspectRatio').value); var wheel = parseFloat(document.getElementById('wheelDiameter').value); if (isNaN(width) || isNaN(ratio) || isNaN(wheel) || width <= 0 || ratio <= 0 || wheel <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // 1. Sidewall height in mm var sidewallMm = width * (ratio / 100); // 2. Wheel diameter in mm (1 inch = 25.4 mm) var wheelMm = wheel * 25.4; // 3. Total Diameter in mm var totalDiameterMm = (sidewallMm * 2) + wheelMm; var totalDiameterIn = totalDiameterMm / 25.4; // 4. Circumference var circumferenceMm = totalDiameterMm * Math.PI; var circumferenceIn = totalDiameterIn * Math.PI; // 5. Revolutions per mile // 1 mile = 63,360 inches var revsPerMile = 63360 / circumferenceIn; // Display results document.getElementById('resTotalDiameter').innerHTML = totalDiameterMm.toFixed(2) + " mm (" + totalDiameterIn.toFixed(2) + " in)"; document.getElementById('resSidewall').innerHTML = sidewallMm.toFixed(2) + " mm (" + (sidewallMm / 25.4).toFixed(2) + " in)"; document.getElementById('resCircumference').innerHTML = circumferenceMm.toFixed(2) + " mm (" + circumferenceIn.toFixed(2) + " in)"; document.getElementById('resRevs').innerHTML = Math.round(revsPerMile).toLocaleString(); document.getElementById('resultsArea').style.display = 'block'; }

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