Tire Size Calculator
Calculate tire dimensions from metric tire size notation.
Results
Metric tire sizes like 225/45R17 pack a lot of information into a short code but they are not intuitive to decode. The first number is tread width in millimeters, the second is sidewall height as a percentage of width and R means radial with the rim diameter in inches. This calculator does the geometry so you can compare tire sizes, check fitment or figure out how a tire swap affects your speedometer.
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Frequently asked questions
The 225 is tread width in mm, 45 is the aspect ratio (sidewall is 45% of width = 101.25 mm) and R17 means a radial tire on a 17-inch rim. Overall diameter is about 634 mm or 25 inches.
Lower aspect ratios (40-45) mean shorter sidewalls which give sharper handling but a firmer ride. Higher ratios (55-70) have taller sidewalls that absorb bumps better but feel less responsive in turns.
Yes. A larger overall diameter means your speedometer reads slower than actual speed. A 3% increase in diameter makes your speedometer read about 3% low. Keep diameter changes within 3% of stock.
Sidewall height = width x aspect ratio / 100. Overall diameter = (sidewall x 2) + (rim diameter x 25.4). For 225/45R17: sidewall is 101.25 mm and diameter is 634.3 mm.
Circumference tells you the distance covered per wheel revolution. It is essential for calculating speedometer error, gear ratio changes and revolutions per mile when comparing tire sizes.