Tire size calculator
Type the size printed on your tire's sidewall, such as 225/65R17, to see what it measures. Add a second size to compare them side by side and see how much a change would affect your speedometer.
Printed on the sidewall, and on the placard in the driver's door jamb.
Common sizes
Drawn to scale
Side view and tread width, nominal sizes
Dimensions
- Overall diameter (height)
- 28.52 in (724 mm)
- Section width
- 8.86 in (225 mm)
- Sidewall height
- 5.76 in (146 mm)
- Rim diameter
- 17 in (432 mm)
- Circumference
- 89.6 in (2,275 mm)
- Revolutions per mile
- 707
- Revolutions per km
- 439
- Aspect ratio
- 65%
Worked out from the size code. Real tires vary a little by brand, tread depth and rim width: the maker's spec sheet lists the measured diameter and revolutions per mile.
Drawn to scale
Side view and tread width, nominal sizes
What 225/65R17 means
- No letter
- A metric (Euro-metric) size. Same dimensions as P-metric, though the load ratings are worked out slightly differently.
- 225
- Section width: 225 mm (8.86 in) from sidewall to sidewall, measured on the tire's measuring rim.
- 65
- Aspect ratio: the sidewall is 65% as tall as the tire is wide, 146 mm (5.76 in).
- R
- Radial construction, which almost every modern car and truck tire uses.
- 17
- Fits a 17-inch wheel (rim diameter).
Sizes with about the same diameter, by rim
Within 3% of 225/65R17 on paper. Pick one to compare. Whether a tire is made in that size, carries your car's load and fits your wheels is a question for a tire professional.
- Nothing is uploaded
- Free, no sign-up
- Works on phone and desktop
How to read and check a tire size
- 1
Find the size on the tire's sidewall, or on the tire placard in the driver's door jamb. It looks like P225/65R17 96H.
- 2
Type it the way it is printed, or loosely: 225/65R17, 225 65 17, LT265/70R17 and flotation sizes like 33x12.50R15 all work.
- 3
Read the overall diameter, width, sidewall height, circumference and revolutions per mile, and see the tire drawn to scale.
- 4
Click Compare with another size, or one of the sizes with a similar diameter, to see the difference and your speedometer error.
Features
Every size format
P-metric, Euro-metric, LT, ST, ZR, C and flotation sizes such as 33x12.50R15LT, typed however you like.
The code explained
Each part of the size, plus the load index in pounds and kilograms and the speed rating in mph and km/h.
Drawn to scale
A side view and tread view of the tire, or of two tires side by side, so a bigger wheel or a taller sidewall is easy to see.
Speedometer error
Compare two sizes to see your real speed when the speedometer shows 25 to 75 mph, and how far off the odometer will be.
How a tire size works
Most car and SUV tires use metric sizing, the system behind both P-metric and Euro-metric sizes. A size such as 225/65R17 gives you three numbers, and the rest follows from them:
- Sidewall height = width × aspect ratio ÷ 100. For 225/65R17: 225 × 0.65 = 146.25 mm (5.76 in).
- Overall diameter = 2 × sidewall + wheel size. Two sidewalls are 292.5 mm, plus 17 × 25.4 = 431.8 mm, which is 724.3 mm or 28.52 in.
- Circumference = π × diameter = 89.6 in, and revolutions per mile = 63,360 ÷ circumference = 707.
Flotation sizes, used for off-road and light-truck tires, are written in inches with the height first: a 33x12.50R15LT is 33 inches tall and 12.5 inches wide on a 15-inch wheel. The sidewall is half of what's left over: (33 − 15) ÷ 2 = 9 inches.
Popular sizes at a glance
| Size | Height | Width | Revs per mile |
|---|---|---|---|
| 205/55R16 | 24.9 in | 8.1 in | 811 |
| 215/55R17 | 26.3 in | 8.5 in | 767 |
| 225/65R17 | 28.5 in | 8.9 in | 707 |
| 235/60R18 | 29.1 in | 9.3 in | 693 |
| 265/70R17 | 31.6 in | 10.4 in | 638 |
| 275/55R20 | 31.9 in | 10.8 in | 632 |
| LT285/75R16 | 32.8 in | 11.2 in | 614 |
| 33x12.50R15LT | 33.0 in | 12.5 in | 611 |
Nominal figures from the size code. Measured sizes differ slightly by brand, tread pattern and the width of the wheel the tire is mounted on.
Load index and speed rating
The number and letter after the size are the service description. The load index is how much weight each tire can carry when properly inflated, from the industry's standard table:
| Load index | Per tire |
|---|---|
| 91 | 1,356 lb (615 kg) |
| 94 | 1,477 lb (670 kg) |
| 96 | 1,565 lb (710 kg) |
| 100 | 1,764 lb (800 kg) |
| 104 | 1,984 lb (900 kg) |
| 112 | 2,469 lb (1,120 kg) |
| 121 | 3,197 lb (1,450 kg) |
The speed rating is the top speed the tire is rated for under test conditions, not a safe cruising speed:
| Rating | Up to |
|---|---|
| Q | 99 mph (160 km/h) |
| R | 106 mph (170 km/h) |
| S | 112 mph (180 km/h) |
| T | 118 mph (190 km/h) |
| H | 130 mph (210 km/h) |
| V | 149 mph (240 km/h) |
| W | 168 mph (270 km/h) |
| Y | 186 mph (300 km/h) |
Replacement tires should generally match or beat the original load index and speed rating. ZR in the size means the tire is rated above 149 mph (240 km/h), and a rating in brackets, such as (Y), means above 186 mph.
Where to find your car's tire size
The size your vehicle was built for is on the tire information placard, usually on the driver's door jamb, and in the owner's manual. Some cars carry it inside the fuel door or glove box. The placard also lists the recommended cold tire pressure, which is not the maximum pressure molded into the sidewall. If the tires on the car don't match the placard, a previous owner may have changed the size: compare the two with the tire size comparison to see how much it changes the speedometer.
A new size also changes how your odometer counts miles, and so your fuel figures. Work out your real mileage with the MPG calculator and plan a trip with the gas cost calculator.
Frequently asked questions
How do I read a tire size?
Take P225/65R17 96H. P means a passenger tire, 225 is the width in millimeters, 65 means the sidewall is 65% as tall as the tire is wide, R is radial construction, and 17 is the wheel diameter in inches. 96 is the load index (710 kg or 1,565 lb per tire) and H is the speed rating (130 mph).
How tall is a 225/65R17 tire?
About 28.5 inches (724 mm). Each sidewall is 225 × 0.65 = 146.3 mm, so the height is two sidewalls plus the 17-inch (431.8 mm) wheel. That is the nominal size; a real tire can differ by a few millimeters.
What does the aspect ratio mean?
It is the sidewall height as a percentage of the width. A 65 series tire has a sidewall 65% as tall as it is wide, a 40 series one only 40%. A lower number means a shorter, stiffer sidewall, usually on a bigger wheel.
Can I put a different tire size on my car?
Often, within limits. The sizes on the tire placard and in the owner's manual are what the vehicle was designed for. A common rule of thumb is to stay within about 3% of the original overall diameter, with a load index and speed rating at least as high as the original, and enough clearance. A tire professional can confirm what fits your vehicle.
What is the difference between P-metric, Euro-metric and LT tires?
P-metric (P225/65R17) is the US system for passenger tires; Euro-metric (225/65R17) has the same dimensions but rates load slightly differently, so check the load index when you swap one for the other. LT tires are built for heavier loads and towing, and are rated with a load range and often a dual-wheel load index.
How many revolutions per mile does a tire make?
Divide 63,360 (inches in a mile) by the circumference in inches. A 225/65R17 is about 89.6 inches around, so it turns about 707 times a mile. Tire makers publish a measured figure that is usually a little different, because a tire flattens slightly under the car's weight.
What is 33x12.50R15 in metric?
33 inches (838 mm) tall, 12.5 inches (318 mm) wide, on a 15-inch wheel, with a 9-inch sidewall. Flotation sizes give the height first. On paper LT305/75R15 is almost exactly as tall, though real tires of both sizes vary by brand.
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