TireSizeCalc Tip

How to read a tire size

In P215/65R15 95H, P means passenger tire (LT is light truck and ST special trailer; no letter is the European metric size). 215 is the section width in millimetres, 65 is the aspect ratio — the sidewall is 65% of the width — R means radial construction and 15 is the wheel diameter in inches. 95 is the load index (690 kg per tire) and H the speed rating (130 mph / 210 km/h). TireSizeCalc decodes the size part and shows the dimensions it implies.

Metric (225/45R17) or flotation (33x12.50R15) sizes

    Similar sizes

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    ZR in a size such as 245/40ZR18 marks a tire rated above 149 mph (240 km/h). The load and speed codes after the size do not change the dimensions.

    How the tire size calculator works

    For a metric size W/A R D, the sidewall height is W × A ÷ 100 millimetres and the overall diameter is D × 25.4 + 2 × sidewall. Circumference = π × diameter, revolutions per mile = 63,360 ÷ circumference in inches, and revolutions per km = 1,000,000 ÷ circumference in mm. With a new tire fitted, actual speed = speedometer reading × new diameter ÷ old diameter.

    Common tire sizes in inches

    SizeDiameterWidthSidewallRevs per mile
    195/65R1524.98″7.68″4.99″807
    205/55R1624.88″8.07″4.44″811
    215/55R1726.31″8.46″4.66″767
    225/45R1724.97″8.86″3.99″808
    225/65R1728.52″8.86″5.76″707
    235/55R1828.18″9.25″5.09″716
    245/40R1825.72″9.65″3.86″784
    265/70R1731.61″10.43″7.3″638
    275/55R2031.91″10.83″5.95″632
    285/75R1632.83″11.22″8.42″614

    TireSizeCalc calculates from the nominal size code (ISO / ETRTO metric and Tire and Rim Association P-metric and LT conventions). Actual dimensions differ by brand, tread depth, wheel width and load; manufacturers' spec sheets list the measured diameter and revolutions per mile. The ±3% guideline is a common rule of thumb, not a legal limit: check your vehicle's placard, load index, speed rating and clearance before changing size.

    Frequently asked questions

    What does the 65 mean in 215/65R15?

    The aspect ratio: the sidewall height is 65% of the 215 mm width, about 140 mm.

    What do the P and LT mean?

    P is a P-metric passenger tire and LT a light-truck tire with a different load rating system. Sizes without a letter are Euro-metric.

    Where do I find the right size for my car?

    On the tire placard inside the driver’s door jamb, in the owner’s manual, or on the sidewall of the original tires.

    Is TireSizeCalc free?

    Yes, with no sign-up or ads.

    Are my sizes saved?

    Yes, in this browser only.

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