Tire and Wheel Size Calculator
One sidewall code, read as a wheel: the rim diameter it mounts on, the sidewall that sits above and below it, and the overall diameter of the two together as they stand on the road, with the circumference and revolutions per mile that follow. Every length is given in inches and millimetres at once, because the code mixes the two and the arithmetic should not make you convert anything by hand.
Rim and tire
- Section width
- 225 mm (8.86 in)
- Sidewall (45%)
- 3.99 in (101.3 mm)
- Rim diameter
- 17 in (431.8 mm)
- Overall diameter
- 24.97 in (634.3 mm)
- Circumference
- 78.45 in (1992.7 mm)
- Revolutions per mile
- 808
Wheel as it stands
- Rim
- 17 in (431.8 mm)
- Sidewall, twice
- 7.97 in (202.5 mm)
- Overall wheel diameter
- 24.97 in (634.3 mm)
- Circumference
- 78.45 in (1992.7 mm)
- Revolutions per mile
- 808
The rim diameter and the tire on it, added into the diameter of the wheel as it stands.
225/45R17 in full
Geometry, not fitment. The page renders no will-it-fit verdict, no clearance claim, no load or speed rating suggestion and no inflation pressure, and it holds no vehicle size table. 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.
Common questions
- What is the difference between wheel size and tire size?
- The wheel is the metal part, and the number in the code that belongs to it is the rim diameter in inches: the 17 in 225/45R17. The tire wraps around it, adding a sidewall at the top and one at the bottom. Overall wheel diameter, the figure that decides how the car sits and how far it travels per turn, is the rim plus both sidewalls, and that is what this page leads with.
- How do I work out the overall diameter of a wheel and tire?
- Take the sidewall height in millimetres, which is the section width times the aspect ratio, convert it at 25.4 mm to the inch, double it and add the rim diameter. For 225/45R17: 101.25 mm of sidewall is 3.99 inches, twice that is 7.97, plus 17 inches of rim gives 24.97 inches overall. The page does that as you type and shows the working.
- What is plus sizing?
- Fitting a larger rim with a lower profile tire so the overall diameter stays close to what it was. 205/55R16 is 24.88 inches overall and 225/45R17 is 24.97: an inch more wheel, a lower sidewall, and only 0.09 of an inch of extra diameter, which is 0.38 percent. Put both codes into the compare page and it gives you that percentage directly.
- Does the code tell me the wheel width?
- No. A tire code carries the rim diameter and nothing about the rim width, which is stamped on the wheel itself, usually as something like 7.5J. Section width and rim width are related, since a wider rim stretches the tire a little, but the code cannot give you either the rim width or the range of rim widths a tire is meant for. This page reports only what the code defines.
- Is the rim diameter in inches even on a metric tire?
- Yes, on the metric codes you will meet on a car. The width is millimetres and the last number is inches, which looks inconsistent and is simply how the standard settled. A handful of true metric sizes exist where the rim is given in millimetres, such as the old TD and TRX fitments, and they are written differently; this page reads the ordinary metric code.
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.