Tire Size Calculator
Enter a tire size to get its overall diameter, sidewall height, circumference, and revolutions per mile. A free tire size calculator for planning plus-sizes and checking tire height before you buy.
Tire Specs
Tire Diagram
Scaled front view — overall diameter, the wheel (dashed), and section width.
How tire sizes work
A tire size like 245/40R18 means a 245 mm section width, a sidewall that is 40% of that width, mounted on an 18 inch wheel. Overall diameter drives your speedometer reading, ride height, and clearance — keep a new size within about 3% of stock for accuracy.
Use this tire size calculator to plan a plus-size or check tire height. Pair it with our tire size comparison and wheel fitment calculator, then shop tires and wheels that fit your build.
Tire size chart: common sizes for 15–24 inch wheels
The 36 sizes below are, for each wheel diameter, the four sizes with the most tires in our catalog. Every number is worked out with the same math the calculator above uses:
- Sidewall height (mm) = section width × aspect ratio ÷ 100
- Overall diameter (in) = wheel diameter + 2 × sidewall height ÷ 25.4
- Circumference (in) = π (3.1416) × overall diameter
- Revolutions per mile = 63,360 ÷ circumference
Flotation truck sizes such as 33x12.50R20 give the overall diameter (33 in) and width (12.50 in) directly; sidewall = (diameter − wheel diameter) ÷ 2. Real tires can measure a little different from the math because of tread depth, construction and rim width, so use the tire maker’s spec sheet for tight clearance checks.
| Size | Width (mm) | Width (in) | Sidewall (mm) | Sidewall (in) | Diameter (in) | Circumference (in) | Revs per mile |
|---|---|---|---|---|---|---|---|
| 15-inch wheels | |||||||
| 185/60R15 | 185 | 7.3 | 111 | 4.37 | 23.74 | 74.6 | 850 |
| 185/65R15 | 185 | 7.3 | 120 | 4.73 | 24.47 | 76.9 | 824 |
| 195/65R15 | 195 | 7.7 | 127 | 4.99 | 24.98 | 78.5 | 807 |
| 235/75R15 | 235 | 9.3 | 176 | 6.94 | 28.88 | 90.7 | 698 |
| 16-inch wheels | |||||||
| 205/55R16 | 205 | 8.1 | 113 | 4.44 | 24.88 | 78.2 | 811 |
| 215/60R16 | 215 | 8.5 | 129 | 5.08 | 26.16 | 82.2 | 771 |
| 245/75R16 | 245 | 9.6 | 184 | 7.23 | 30.47 | 95.7 | 662 |
| 265/75R16 | 265 | 10.4 | 199 | 7.82 | 31.65 | 99.4 | 637 |
| 17-inch wheels | |||||||
| 225/45R17 | 225 | 8.9 | 101 | 3.99 | 24.97 | 78.5 | 808 |
| 225/50R17 | 225 | 8.9 | 113 | 4.43 | 25.86 | 81.2 | 780 |
| 225/65R17 | 225 | 8.9 | 146 | 5.76 | 28.52 | 89.6 | 707 |
| 265/70R17 | 265 | 10.4 | 186 | 7.30 | 31.61 | 99.3 | 638 |
| 18-inch wheels | |||||||
| 225/45R18 | 225 | 8.9 | 101 | 3.99 | 25.97 | 81.6 | 777 |
| 235/60R18 | 235 | 9.3 | 141 | 5.55 | 29.10 | 91.4 | 693 |
| 245/40R18 | 245 | 9.6 | 98 | 3.86 | 25.72 | 80.8 | 784 |
| 275/65R18 | 275 | 10.8 | 179 | 7.04 | 32.07 | 100.8 | 629 |
| 19-inch wheels | |||||||
| 235/40R19 | 235 | 9.3 | 94 | 3.70 | 26.40 | 82.9 | 764 |
| 235/55R19 | 235 | 9.3 | 129 | 5.09 | 29.18 | 91.7 | 691 |
| 245/40R19 | 245 | 9.6 | 98 | 3.86 | 26.72 | 83.9 | 755 |
| 245/45R19 | 245 | 9.6 | 110 | 4.34 | 27.68 | 87.0 | 729 |
| 20-inch wheels | |||||||
| 245/45R20 | 245 | 9.6 | 110 | 4.34 | 28.68 | 90.1 | 703 |
| 275/40R20 | 275 | 10.8 | 110 | 4.33 | 28.66 | 90.0 | 704 |
| 275/55R20 | 275 | 10.8 | 151 | 5.95 | 31.91 | 100.2 | 632 |
| 275/60R20 | 275 | 10.8 | 165 | 6.50 | 32.99 | 103.6 | 611 |
| 21-inch wheels | |||||||
| 265/40R21 | 265 | 10.4 | 106 | 4.17 | 29.35 | 92.2 | 687 |
| 275/35R21 | 275 | 10.8 | 96 | 3.79 | 28.58 | 89.8 | 706 |
| 275/45R21 | 275 | 10.8 | 124 | 4.87 | 30.74 | 96.6 | 656 |
| 295/35R21 | 295 | 11.6 | 103 | 4.06 | 29.13 | 91.5 | 692 |
| 22-inch wheels | |||||||
| 265/35R22 | 265 | 10.4 | 93 | 3.65 | 29.30 | 92.1 | 688 |
| 275/40R22 | 275 | 10.8 | 110 | 4.33 | 30.66 | 96.3 | 658 |
| 285/40R22 | 285 | 11.2 | 114 | 4.49 | 30.98 | 97.3 | 651 |
| 285/45R22 | 285 | 11.2 | 128 | 5.05 | 32.10 | 100.8 | 628 |
| 24-inch wheels | |||||||
| 255/30R24 | 255 | 10.0 | 77 | 3.01 | 30.02 | 94.3 | 672 |
| 275/25R24 | 275 | 10.8 | 69 | 2.71 | 29.41 | 92.4 | 686 |
| 295/35R24 | 295 | 11.6 | 103 | 4.06 | 32.13 | 100.9 | 628 |
| 305/35R24 | 305 | 12.0 | 107 | 4.20 | 32.41 | 101.8 | 622 |
Need a size that is not here? Type it into the calculator above.
How to read a tire size
Every tire has its size molded into the sidewall. The same size is printed on the sticker in the driver’s door jamb, which shows what your vehicle came with. Here is what each part means.
- Tire type (P or LT). “P” means a passenger tire. “LT” means a light-truck tire, built heavier to carry more weight and usually run at higher pressure. No letter at all means a metric (European) size, which is sized the same way as P-metric.
- Section width. The first number is the width of the tire from sidewall to sidewall, in millimeters.
- Aspect ratio. The number after the slash is the sidewall height as a percentage of the width. A 45 means the sidewall is 45% as tall as the tire is wide.
- Construction. “R” means radial, which is almost every tire sold today. “ZR” marks a tire built for speeds above 149 mph. “D” or “B” means bias-ply.
- Wheel (rim) diameter. The number after the R is the wheel size the tire fits, in inches.
- Load index. The number after the size is how much weight each tire can carry at its maximum pressure. 91 = 1,356 lb, 100 = 1,764 lb, 121 = 3,197 lb.
- Speed rating. The letter at the end is the highest speed the tire is rated to hold: S = 112 mph, T = 118, H = 130, V = 149, W = 168, Y = 186.
Flotation truck sizes read differently. In 33x12.50R20, 33 is the overall height in inches, 12.50 is the width in inches and 20 is the wheel size.
Example 1: P225/45R17 91V
| P | Passenger tire |
|---|---|
| 225 | 225 mm wide (8.9 in) |
| 45 | Sidewall is 45% of 225 = 101.25 mm (3.99 in) |
| R17 | Radial, fits a 17 inch wheel |
| 91 | Carries up to 1,356 lb per tire |
| V | Rated to 149 mph |
| Height | 17 + 2 × 3.99 = 24.97 in tall, 808 revolutions per mile |
Example 2: LT265/70R17 121/118S
| LT | Light-truck tire (this one is Load Range E) |
|---|---|
| 265 | 265 mm wide (10.4 in) |
| 70 | Sidewall is 70% of 265 = 185.5 mm (7.30 in) |
| R17 | Radial, fits a 17 inch wheel |
| 121/118 | 3,197 lb per tire as a single, 2,910 lb per tire in a dual-rear setup |
| S | Rated to 112 mph |
| Height | 17 + 2 × 7.30 = 31.61 in tall, 638 revolutions per mile |
Common questions
How much bigger can I go before my speedometer is off?
Most shops keep a new size within about 3% of the original overall diameter. Past that, the speedometer error is easy to notice and you may need a recalibration. Going from 265/70R17 (31.61 in) to 285/70R17 (32.71 in) is 3.5% taller: when the speedometer reads 60 mph you are really doing 62.1 mph. The tire size comparison tool shows this for any two sizes.
What size is a 33 inch tire in metric?
Any size that works out to about 33 inches tall. From the chart: 285/75R16 (32.83 in), 275/70R18 (33.16 in), 275/60R20 (32.99 in), 275/50R22 (32.83 in), 305/45R22 (32.81 in). On a 20 inch wheel, 275/60R20 is the classic “metric 33”.
Does a wider tire make the tire taller?
Yes, if the aspect ratio stays the same, because the sidewall is a percentage of the width. 245/40R18 is 25.72 in tall; 275/40R18 is 26.66 in, about 0.9 in taller. To go wider without going taller, drop the aspect ratio, for example 275/35R18 (25.58 in).
What do revolutions per mile tell me?
How many times the tire turns in one mile. A taller tire turns fewer times: 265/70R17 turns 638 times a mile, 285/75R17 turns 596. Fewer turns means the speedometer reads low and the engine turns slower at the same road speed, which can make a truck feel less eager.
Can I use a different size than the one on my door sticker?
Usually, as long as the new size stays within about 3% of the original height, fits the wheel width, clears the suspension and fenders, and has a load index and speed rating at least as high as the original. Our wheel fitment calculator checks a full wheel and tire setup against your stock one.
What is the difference between P-metric and LT tires?
LT tires are built with stiffer sidewalls and more plies to carry heavier loads, and they use their own load table. They usually need higher inflation pressure than a P-metric tire of the same size to carry the same weight, so follow the tire maker’s load and pressure chart when you switch.
More tire and wheel tools
Plan the rest of the setup with the tools that use the same math.