How to use the tire size calculator
- Find the size on the tire's sidewall, or on the placard inside the driver's door jamb. It looks like 265/70R17 or, on many truck tires, 33x12.50R17.
- Type or paste it into the box. Letters before or after the size (P, LT, ST) and the load and speed code (such as 113T) are fine: the calculator ignores what it doesn't need.
- Read the overall diameter (tire height), section width, sidewall height, circumference and revolutions per mile, in inches and millimeters, with a to-scale drawing.
- Scroll down for equivalent tire sizes: sizes on the same, smaller or larger wheels that stay within 3% of the height.
How to read a tire size (what the numbers mean)
Take P225/60R16 97T, a common passenger car size:
- P: tire type. P = passenger (P-metric), LT = light truck, ST = special trailer. No letter means a Euro-metric size.
- 225: section width in millimeters, sidewall to sidewall (8.86 in).
- 60: aspect ratio. The sidewall height is 60% of the width: 225 × 0.60 = 135 mm (5.31 in).
- R: radial construction (almost every modern tire). ZR marks older high-speed sizes; D means bias-ply.
- 16: wheel (rim) diameter in inches.
- 97T: the service description. 97 is the load index (1,609 lb per tire) and T is the speed rating (118 mph). They don't affect the dimensions.
So a P225/60R16 is 26.63 in tall. Flotation sizes such as 33x12.50R17 are read directly in inches: 33 in tall, 12.50 in wide, for a 17 in wheel.
How to calculate tire diameter
Sidewall height = width × aspect ratio ÷ 100, and tire diameter = wheel diameter + 2 × sidewall height. Because the width is in millimeters and the wheel in inches, divide the sidewall by 25.4 first. For 265/70R17:
- Sidewall: 265 × 0.70 = 185.5 mm ÷ 25.4 = 7.30 in
- Diameter: 17 + 2 × 7.3 = 31.61 in (803 mm)
- Circumference: π × 31.61 = 99.29 in, so about 638 revolutions per mile (63,360 ÷ circumference)
Metric to inch tire size conversion
To convert a metric size to inches, use the diameter and the width: 265/70R17 is 31.6x10.4R17 (about 31.6 in tall and 10.4 in wide). To go the other way, width in mm = inches × 25.4, and aspect ratio = sidewall ÷ width. That makes 35x12.50R20 roughly 318/60R20. Converted sizes are approximate: pick a real size from a tire maker's range and check it in the tire size comparison.
Tire size chart
Dimensions of popular car, SUV and truck sizes, calculated from the size code (new tire, unloaded).
| Tire size | Diameter | Width | Sidewall | Revs/mile |
|---|---|---|---|---|
| 15-inch wheels | ||||
| 195/65R15 | 25.0 in | 7.7 in | 5.0 in | 807 |
| 205/65R15 | 25.5 in | 8.1 in | 5.2 in | 791 |
| 215/70R15 | 26.9 in | 8.5 in | 5.9 in | 751 |
| 235/75R15 | 28.9 in | 9.3 in | 6.9 in | 698 |
| 16-inch wheels | ||||
| 205/55R16 | 24.9 in | 8.1 in | 4.4 in | 811 |
| 215/60R16 | 26.2 in | 8.5 in | 5.1 in | 771 |
| 225/70R16 | 28.4 in | 8.9 in | 6.2 in | 710 |
| 245/75R16 | 30.5 in | 9.6 in | 7.2 in | 662 |
| 265/75R16 | 31.6 in | 10.4 in | 7.8 in | 637 |
| 285/75R16 | 32.8 in | 11.2 in | 8.4 in | 614 |
| 17-inch wheels | ||||
| 215/55R17 | 26.3 in | 8.5 in | 4.7 in | 767 |
| 225/65R17 | 28.5 in | 8.9 in | 5.8 in | 707 |
| 235/65R17 | 29.0 in | 9.3 in | 6.0 in | 695 |
| 245/70R17 | 30.5 in | 9.6 in | 6.8 in | 661 |
| 265/70R17 | 31.6 in | 10.4 in | 7.3 in | 638 |
| 285/70R17 | 32.7 in | 11.2 in | 7.9 in | 617 |
| 315/70R17 | 34.4 in | 12.4 in | 8.7 in | 587 |
| 18-inch wheels | ||||
| 225/45R18 | 26.0 in | 8.9 in | 4.0 in | 777 |
| 235/60R18 | 29.1 in | 9.3 in | 5.6 in | 693 |
| 245/60R18 | 29.6 in | 9.6 in | 5.8 in | 682 |
| 265/65R18 | 31.6 in | 10.4 in | 6.8 in | 639 |
| 275/65R18 | 32.1 in | 10.8 in | 7.0 in | 629 |
| 285/65R18 | 32.6 in | 11.2 in | 7.3 in | 619 |
| 19-inch wheels | ||||
| 245/45R19 | 27.7 in | 9.6 in | 4.3 in | 729 |
| 255/55R19 | 30.0 in | 10.0 in | 5.5 in | 671 |
| 20-inch wheels | ||||
| 245/45R20 | 28.7 in | 9.6 in | 4.3 in | 703 |
| 255/55R20 | 31.0 in | 10.0 in | 5.5 in | 650 |
| 275/55R20 | 31.9 in | 10.8 in | 6.0 in | 632 |
| 275/60R20 | 33.0 in | 10.8 in | 6.5 in | 611 |
| 275/65R20 | 34.1 in | 10.8 in | 7.0 in | 592 |
| 285/55R20 | 32.3 in | 11.2 in | 6.2 in | 624 |
| 22-inch wheels | ||||
| 285/45R22 | 32.1 in | 11.2 in | 5.0 in | 628 |
| 305/45R22 | 32.8 in | 12.0 in | 5.4 in | 615 |
| Flotation (inch) sizes | ||||
| 31x10.50R15 | 31.0 in | 10.5 in | 8.0 in | 651 |
| 33x12.50R15 | 33.0 in | 12.5 in | 9.0 in | 611 |
| 33x12.50R17 | 33.0 in | 12.5 in | 8.0 in | 611 |
| 33x12.50R20 | 33.0 in | 12.5 in | 6.5 in | 611 |
| 35x12.50R17 | 35.0 in | 12.5 in | 9.0 in | 576 |
| 35x12.50R20 | 35.0 in | 12.5 in | 7.5 in | 576 |
| 37x12.50R17 | 37.0 in | 12.5 in | 10.0 in | 545 |
Equivalent tire sizes and plus sizing
Changing wheel size ("plus sizing") works when the overall diameter stays close to the original. Most tire shops aim for within ±3%. Go up an inch in wheel diameter and you need a lower aspect ratio (a shorter sidewall), often with a slightly wider tire, to keep the same height. For 265/70R17 (31.6 in):
- 18-inch wheels: 265/65R18 is 31.6 in (−0.1%)
- 20-inch wheels: 265/55R20 is 31.5 in (−0.4%)
The calculator lists every standard metric size within 3% for your tire. Before you buy, confirm the size is actually made, fits your wheel width and has at least the original load index and speed rating.
Related tire and wheel tools
- Tire size comparison: put your current and new sizes side by side, with height, width, ride height and speedometer difference.
- Speedometer calculator: your true speed after bigger tires or a gear change.
- Wheel offset calculator: how far new wheels poke out or tuck in, and offset to backspacing.
Frequently asked questions
How do you calculate tire diameter from the size?
Tire diameter = rim diameter + 2 × sidewall height, where sidewall height = width × aspect ratio ÷ 100 (in mm; divide by 25.4 for inches). For 265/70R17: 265 × 0.70 = 185.5 mm = 7.30 in of sidewall, so the diameter is 17 + 2 × 7.3 = 31.61 in.
What does 265/70R17 mean?
265 is the tire's section width in millimeters. 70 is the aspect ratio: the sidewall is 70% as tall as the tire is wide. R means radial construction, and 17 is the wheel (rim) diameter in inches. Put together, 265/70R17 is about 31.6 in tall and 10.4 in wide.
How tall is a 265/70R17 tire in inches?
31.61 in (803 mm) when new and unloaded, which is why it's often called a "31.6-inch" tire. In inch sizing it's roughly 31.6x10.4R17.
What size is a 33 inch tire in metric?
On 17-inch wheels, the metric sizes sold as "33s" are 285/70R17 (32.7 in tall) and 295/70R17 (33.3 in). A true flotation size such as 33x12.50R17 is exactly 33 inches tall and 12.5 inches wide. Enter any size above to see its exact height.
How do you convert a flotation size like 35x12.50R20 to metric?
The first number is the height (35 in), the second is the width (12.50 in) and the last is the rim (20 in). Width in mm = 12.50 × 25.4 = 318 mm, and the sidewall is (35 − 20) ÷ 2 = 7.5 in, which is 60% of the width. So 35x12.50R20 is roughly 318/60R20.
What is an equivalent tire size?
A different size with nearly the same overall diameter, usually within 3%, so your speedometer and gearing stay close to stock. For 265/70R17 (31.6 in), 265/65R18 on an 18-inch wheel is 31.6 in (−0.1%) and 265/55R20 on a 20-inch wheel is 31.5 in (−0.4%).
What do P, LT and ST mean at the start of a tire size?
P is a P-metric passenger tire, LT is a light-truck tire (stiffer, higher load ratings, often with a load range letter), and ST is a special-trailer tire that should only be used on trailers. A size with no letter is Euro-metric. The letter doesn't change the dimensions, only the load and use rating.
How many revolutions per mile does a tire make?
Revolutions per mile = 63,360 ÷ circumference in inches. 265/70R17 has a 99.3 in circumference, so about 638 revolutions per mile. Manufacturers quote a slightly higher figure, because a loaded tire squats a little and rolls on a smaller radius.
Can I put a different size tire on my car?
Usually, if the new size stays within about 3% of the original diameter, fits your wheel width, clears the suspension and body at full lock and full compression, and has a load index and speed rating at least as high as the original. Bigger changes affect the speedometer, ABS and traction control, and gearing. Check the tire placard in the driver's door jamb for your original size.
Is my data saved or sent anywhere?
Your entries are saved only in your own browser so they are there next time. Nothing is sent to our servers.