Tire Height Calculator
Type one sidewall code and the page leads with the two numbers people mean by height: the overall diameter of the tire and the sidewall height on each side, in inches and millimetres together, with the section width, circumference and revolutions per mile under them. The working is written out beside it, so you can see the sidewall come from the aspect ratio and the diameter come from the rim plus two sidewalls.
- Overall diameter
- 24.97 in (634.3 mm)
- Sidewall (45%)
- 3.99 in (101.3 mm)
- Section width
- 225 mm (8.86 in)
- Rim diameter
- 17 in (431.8 mm)
- Circumference
- 78.45 in (1992.7 mm)
- Revolutions per mile
- 808
sidewall = 225 mm x 45% = 101.25 mm = 101.25 / 25.4 = 3.99 in diameter = 17 + 2 x 3.99 = 24.97 in circumf. = pi x 24.97 = 78.45 in revs/mile = 63360 / 78.45 = 808
One code read out in full: overall diameter, sidewall height, section width, circumference.
225/45R17 in full
Common questions
- How tall is a 225/45R17?
- 24.97 inches, or 634.3 mm, over the whole tire. The sidewall is 45 percent of 225 mm, which is 101.25 mm or 3.99 inches, and there is one of those above the rim and one below, so the overall diameter is 17 inches plus 7.97 inches. Any other code works the same way: type it in and the page shows both figures.
- Is tire height the same as tire diameter?
- People usually say height and mean the overall diameter, which is what a lift, a wheel well or a gearing calculation needs. Sidewall height is a different number: the depth of rubber on one side, between the rim and the tread. This page leads with both so there is no guessing which one you have been given, and labels them plainly.
- How do I work the height out from the code myself?
- Multiply the section width by the aspect ratio to get the sidewall in millimetres, divide by 25.4 for inches, double it because there is a sidewall at the top and the bottom, then add the rim diameter. For 265/70R17: 265 times 70 percent is 185.5 mm, which is 7.30 inches, doubled is 14.61, plus 17 is 31.61 inches. The inch is exactly 25.4 mm, so nothing in that chain is rounded until it is displayed.
- Will my tire really measure that tall?
- Close, but not to the decimal. The code defines a nominal size on a reference rim; a mounted tire's true diameter moves with inflation pressure, the load on it, the width of the rim it is on, tread wear and the maker's own tolerance. Treat the figure as the design dimension, which is what every calculator and every catalogue is quoting, and measure the tire if you need the real one.
- Why is the width in millimetres and the rim in inches?
- History: the metric code was standardised on tires while wheels stayed on the inch sizes the industry already had. So 225/45R17 is 225 mm across, 45 percent of that in sidewall, on a 17 inch wheel. The page converts everything both ways so you never have to hold two unit systems in your head.
Exact arithmetic on the sidewall code, which is a definition rather than an estimate. It cannot know your wheel well's clearance, whether a load or speed rating suits your vehicle, or the true mounted diameter, which changes with pressure, load and wear.