Installing the correct size tires on your vehicle is critical to its performance. A common issue is that not everyone knows how to read the tire size. With many numbers and letters listed on the tire sidewall, it can be hard to understand what they mean.
This article will explain all of the tire sidewall specifications so that you will understand what the tire size means and all of the information.
How to Read a Tire Size (Example: 225/50R16)
The most prominent information on a tire sidewall is the tire size. Passenger car tire sizes are expressed with a series of numbers and letters, such as 225/50R16. Here’s what each part represents:
- 225 is the width of the tire in millimeters from sidewall to sidewall
- 50 is the aspect ratio, which is sidewall height as a percentage of width (a lower number means a shorter sidewall)
- R indicates radial construction
- 16 is the diameter of the wheel rim in inches
So a tire size of 225/50R16 translates to a tire that is 225 millimeters wide with a sidewall height that is 50 percent of the width, has a radial construction, and fits 16-inch wheels.
By understanding what the numbers on your tire sidewall mean, you’ll be better equipped to select tires that are right for your specific vehicle, driving needs, and conditions.
Key Tire Measurement Terms Explained
Before diving into charts, it helps to understand the key measurements you’ll see:
- Section Width – How wide the tire is from sidewall to sidewall, usually in millimeters.
- Aspect Ratio – The sidewall height as a percentage of the section width. A larger number = taller sidewall.
- Wheel Size – The diameter of the rim the tire fits, in inches.
- Sidewall Height – The actual height of the tire’s sidewall, from the rim to the tread.
- Overall Diameter – The total height of the tire from the ground to the top of the tread.
- Circumference – The distance around the tire. This affects speedometer readings and gearing.
- Revolutions per Mile (Revs/Mile) – How many times the tire rotates in one mile. Smaller tires spin more times per mile; larger tires spin fewer times.
Tire Size Explained
The three numbers you will find on the tire’s sidewall represent the width, height, and diameter of the tire, respectively. The width is measured in millimetres and indicates how wide the tire is from side to side.
The height is measured in a height-to-width ratio. The diameter is measured in inches and tells you the size of the rim or wheel that the tire will fit onto.
For example, a tire with a width of 225, a height of 50, and a diameter of 15 would be considered a 225/50/15 tire.
Every tire sidewall contains the tire type, tire width, aspect ratio, and construction. It also contains the wheel diameter, load index, speed rating, DOT symbol, TIN, and UTQG information. This data must be used together to determine if it’s the right tire for your vehicle.
#1. Tire Type.
P225/65R15 95H
Most car tires have the letter “P” at the front of the tire size. This letter signifies that it is a P-Metric tire designed for the standards of passenger vehicles.
The first letter in the code tells you what class of tire it is.
- P stands for passenger vehicle tire. P-class tires include cars, SUVs, crossovers, minivans, and smaller pickup trucks, as well as EVs (electric vehicles). While the right load capacity can be achieved for electric vehicles with a standard passenger vehicle tire, special EV tires may be available for some vehicles. Look for the letters EV on the sidewall.
- LT means light truck tire, designed for vehicles capable of carrying heavy loads, towing trailers, or for those looking for an extra heavy-duty option. These are often equipped on three-quarter or 1-ton trucks and SUVs.
- ST stands for Special Trailer. These tire sizes are meant for trailers, including fifth wheels and other travel trailers, as well as boat and utility trailers.
If there’s no letter before the first number, you have a metric tire, most commonly referred to as European size. It’s also measured in millimeters, but may have a different load capacity than a P or LT tire. Confused by all the numbers and letters?
#2. Tire Width.
P225/65R15 95H
The tire is measured by its width. This measurement is given in millimetres, based on how much room there is between each sidewall. This can also be referred to as the section width.
In the tire size, the first three numbers refer to the width of the tire. As an example, if your tire size is P225/65R15, the width of the tire would be 225 millimetres.
#3. Aspect Ratio.
P225/65R15 95H
After the slash mark, the next number you will see is the tire’s aspect ratio. The aspect ratio of a tire is the height of the cross-section compared to the width. This two-digit number is found after the slash symbol in the tire size.
In the example used above, P225/65R15, the 65 is the aspect ratio. It shows that the height of the tire is equal to 65% of the width. This figure determines how well the vehicle handles your tires. The higher the number is, the longer the response time when turning, while the lower the number, the faster the response to a command.
#4. Construction.
P225/65R15 95H
Most passenger tires feature an “R” after the aspect ratio. This letter signifies that it is a Radial Tire. These tires are the most common on the road and are made by assembling piles of fabric, steel, and polyester, along with coated rubber, lying perpendicular to the direction the tire travels. This design provides the smoothest ride and longer tread life.
There can also be tires with a “D,” standing for Diagonal Piles. These are otherwise referred to as Bias-Constructed Tires, Bias Ply or X-Ply, Cross-Ply, and Conventional Tires. You will find this type most commonly used with trailer or motorcycle tires.
Additionally, some tires feature an “F” before the construction letter. This letter is only found on run-flat varieties.
#5. Wheel Diameter.
P225/65R15 95H
It’s important to know what size wheel the tire is meant for. The final number in the sequence is the diameter of the wheel or rim diameter. This figure shows what size wheel should be used with the tire.
The measurement is determined by figuring out the space across the center, from one size to the next. Usually, this figure is listed in inches, such as 15 inches from our example, P225/65R15.
#6. Load Index.
P225/65R15 95H
The load index is the figure used to show the total weight the tire is capable of handling when it is at full inflation. The higher the number of the tire’s load index rating, the more weight you can put on the tires. However, you can’t easily tell how much weight it holds just by looking at this figure.
Instead, you need to reference a chart that shows you what the load index rating means. As an example, a load capability of 117 means that the tire can handle 2,833 pounds of weight. Most passenger vehicles use load indexes ranging from 70 to 125.
#7. Speed Rating.
P225/65R15 95H
The speed rating or maximum speed rating is another figure that needs to be referenced with the help of a chart. This figure relates to the top speed capability you can use the tire at. Tires with higher speed ratings provide more control at higher speeds and can handle heat better.
The most common speed ratings for a family sedan, SUVs, and van tires are S and T, translated as 112 or 118 mph. H (130 mph) is commonly used with passenger cars, SUVs, light pickup trucks, coupes, and sports cars. Other light trucks use N, P, Q, or R (87, 93, 99, and 106 mph).
If you drive a high-performance vehicle, you might see a V, W, or Y (149, 168, or 186 mph). Almost all of the winter tires use either the Q, S, or T speed rating. Of course, this is just the tire’s maximum speed capability, and you should always follow the legal speed limits.
#8. DOT Symbol.
Every tire sidewall used in the United States should have the DOT symbol located on the side. The DOT stands for Department of Transportation.
With this symbol, you know that the tire complies with Federal Motor Vehicle Safety Standards. Any reliable manufacturer uses the DOT symbol, so there’s nothing to worry about when you are buying a top brand.
#9. TIN.
Just like your car has an identification number, your tire also contains a serial number. The Tire Identification Number (TIN) tells you everything you need to know about the tire. This number is located after the DOT letters.
The TIN can be eight to 13 letters/numbers to identify the most important aspects of the tire. Not only will it reveal where the tire was made, but it also shows the manufacturer’s code plus the date the tire was manufactured.
#10. UTQG.
The UTQG stands for Uniform Tire Quality Grading. This rating system was made by the Department of Transportation, and it provides you with the data needed to purchase the best tires based on temperature capability, traction, and treadwear.
The traction grade shows the wet traction capability of the tire as performed during controlled testing. The AA-rated tire provides the best traction when driving on wet roads.
The temperature grade shows the ability of the tire to handle and dissipate heat. The higher the temperature grade, the more capable it is of operating at faster speeds. A temperature grade of A can handle speeds over 115 mph.
The treadwear grade shows how the tire responded to government testing. It’s designed to reveal the expected wear of the tire’s tread. The government test course runs 6,000 miles, so it’s long enough to reveal how the tire should wear. A tire with a 150 grade would wear 1.5 times better than a similar tire with a 100 rating. With that in mind, a tire with a rating of 200 would last twice as long as that same 100-grade option.
Still, the wear of a tire is going to depend on far more than what this rating is. Tire performance relies heavily on how the vehicle is driven, the type of roads it is used on, and several other factors. The rating only shows what the tire is capable of.
Is Tire Size Important?
The tires must fit your vehicle correctly for proper usage. The first problem with improperly sized tires is simply the way they look. When you put tires on that are too small or too large for your vehicle, it doesn’t look right.
But there are far more dangerous consequences of the wrong tire size. The tires carry the weight of your car and are the only part touching the road.
You should verify that the tires are rated for your particular vehicle for your on-road safety, or else you risk compromising your safety.
With the wrong tire size, you will feel compromised handling. If you try to turn or hit slippery roads, you might feel a change in your vehicle as well. Finally, tires that are not suited for your vehicle will wear faster, and you will spend money replacing them sooner.
Your car owner’s manual will recommend the tire size for your vehicle. You can also find this information on a placard in the driver’s side door jamb.
Tire Size Examples:
We will look at two popular types of tires and show you how to read them based on the factors above. As we look at these examples, you should be able to determine your own tire sizes using this same formula.
The first example is P225/65R17 100 T. If your tire says that, you would evaluate it based on the following factors:
- Tire Type: In this case, since it has a P, you know it is a passenger tire. This is the most common type of tire on the road.
- Tire Width: The width of the tire is 225 millimeters. This is measured sidewall to sidewall and is expected to be slightly above ten inches. If referred to as a section width.
- Aspect Ratio: The sidewall of the tire is 65% of the width of the tire. Based on that, the sidewall is about 146 millimeters or about 5.75 inches.
- Construction: The R stands for Radial Tire. This is also the most common type of tire on the road.
- Wheel Diameter: The diameter is 17 inches. This is measured edge-to-edge and tells what size wheel to put the tire on.
- Load Index: If the load index of the tire is rated at 100, the tire can carry up to 1,604 pounds.
- Speed Rating: This tire also has a speed rating of T. This tire is good for speeds up to 118 mph.
In review, this P225/65R17 100T tire is a passenger tire that has a width of 225 millimeters. It has an aspect ratio of 65% and a radial construction. It has a 17-inch diameter, can carry 1,604 pounds, and travel at speeds up to 118 mph.
Let’s go through one more example to make sure that you understand. For this example, we will use P275/55R20 111S.
- Tire Type: In this case, since it has a P, you know it is a passenger tire. This is the most common type of tire on the road.
- Tire Width: The width of the tire is 275 millimeters. This is measured sidewall to sidewall and is expected to be slightly shorter than 11 inches.
- Aspect Ratio: The sidewall of the tire is 55% of the width of the tire. Based on that, the sidewall is about 151 millimeters or about 6 inches.
- Construction: The R stands for Radial Tire. This is also the most common type of tire on the road.
- Wheel Diameter: The diameter is 20 inches. This is measured edge-to-edge and tells what size wheel to put the tire on.
- Load Index: If the load index of the tire is rated at 111, the tire can carry up to 2,403 pounds.
- Speed Rating: This tire also has a speed rating of S. This tire is good for speeds up to 112 mph.
In review, this P275/55R20 111S tire is a passenger tire that has a width of 275 millimeters. It has an aspect ratio of 55% and a radial construction. It has a 20-inch diameter, can carry 2,403 pounds, and travel at speeds up to 112 mph.
Where to Find The Tire Size?
When you are getting new tires for your vehicle, you want to make sure you are getting the right tire size. There are two ways to reference the tire size of your vehicle.
One, look at the tires on the vehicle now. One way to match this information is to have the same tires put on your vehicle. But what happens when you discover that someone put the wrong tires on your vehicle before you purchased it?
That is why it is always recommended to go to the door jamb inside the driver’s door. There is a placard that will tell you the correct tire size. Another place to find this information is in your owner’s manual. When you check with the car manufacturer’s specifications, you can’t miss.
What do the 3 numbers mean on tire size?
The 3 numbers on tire size mean width, height, and diameter, in that order. The width is the tire width in millimeters and measures how wide your tire is. The height is calculated in a height-to-width ratio. The diameter is in inches and determines the size of the rim or wheel that the tire will fit on.
For example, if you have a tire that is 225 in width, a height of 50, and a diameter of 17, it is a 225/50/17 tire.
How to read tire size on a truck?
Most trucks use the same tire size system as cars do. The first number in a truck tire size is the width of the tire in millimeters.
The second number is the height or aspect ratio of the tire. The third number is the diameter of the wheel in inches. In the next section, we provide information on truck tire sizes in inches.
How to read tire sizes in inches?
Tire sizes in inches can be a little more complicated than tire sizes in millimeters. For example (35X12 50R18) – The first number of 35 and 12 refer to the diameter and the width of the tire, respectively, while the number 50 would refer to the aspect ratio (the height of the sidewall compared to the width).
The last R18 refers to the rim in inches. So, for this example, a 35X12 50R18 would be a 35-inch tire and would have a width of 12 inches and would fit on an 18-inch rim.
How to read a motorcycle tire size?
Motorcycle tires use the same characteristics for sizes as car tires. The first 3 digits are the width of the tire in millimeters (mm).
The next two digits are the aspect ratio, which refers to height when measured from its cross-section to its width. Last, the final two digits describe the diameter of the motorcycle wheel, in inches.
Tire Size Charts
Below you will find several charts that will help you understand tire sizing numbers, including a load index chart and speed rating chart.
Load Ratings
The load index is the maximum load that the tire can support. The bigger the value, the more load that it can bear when properly inflated. These load indexes correspond to carrying capacities. For instance, in our example, “82” is 1047 lbs.
Note: Light truck tires have two load indexes, unlike passenger tires, because LT tires are mostly used on vehicles with dual rear wheels. The first load index marks the load capacity when used as a single tire. The second index marks the load capacity when used for two tires.
Tires typically range from 70 to 126 for their load index. You can review the table below to find your load index rating and the corresponding carrying capacity.
| Load Index | Max lbs. | Load Index | Max lbs. |
| 71 | 761 | 86 | 1168 |
| 72 | 783 | 87 | 1201 |
| 73 | 805 | 88 | 1235 |
| 74 | 827 | 89 | 1279 |
| 75 | 853 | 90 | 1323 |
| 76 | 882 | 91 | 1356 |
| 77 | 908 | 92 | 1389 |
| 78 | 937 | 93 | 1433 |
| 79 | 963 | 94 | 1477 |
| 80 | 992 | 95 | 1521 |
| 81 | 1019 | 96 | 1565 |
| 82 | 1047 | 97 | 1609 |
| 83 | 1074 | 98 | 1653 |
| 84 | 1102 | 99 | 1709 |
| 85 | 1135 | 100 | 1764 |
| 101 | 1819 | 116 | 2756 |
| 102 | 1874 | 117 | 2833 |
| 103 | 1929 | 118 | 2910 |
| 104 | 1984 | 119 | 2998 |
| 105 | 2039 | 120 | 3086 |
| 106 | 2094 | 121 | 3197 |
| 107 | 2149 | 122 | 3307 |
| 108 | 2205 | 123 | 3417 |
| 109 | 2271 | 124 | 3527 |
| 110 | 2337 | 125 | 3638 |
| 111 | 2403 | 126 | 3748 |
| 112 | 2469 | 127 | 3858 |
| 113 | 2535 | 128 | 3968 |
| 114 | 2601 | 129 | 4079 |
| 115 | 2679 | 130 | 4189 |
LT Load Ranges
| Load Range | Ply Rating | Max Load Pressure |
|---|---|---|
| B | 4 | 35 psi |
| C | 6 | 50 psi |
| D | 8 | 65 psi |
| E | 10 | 80 psi |
| F | 12 | 95 psi |
Passenger Load Ranges
| Load Range | Symbol | Max Load Pressure |
|---|---|---|
| Light Load | LL | 35 psi |
| Standard Load | SL | 35/44 psi |
| Extra Load | XL | 41/50 psi |
Speed Ratings
The speed index rating indicates the ability of the tire to handle a maximum speed corresponding to the maximum load, without suffering any deterioration in performance.
For example, an H rating has a maximum speed capability of 130 mph or 210 km/hr. On the other hand, a ‘Z’ rated tire has no maximum speed. This rating is for more than 149 mph; Sports cars mostly use the Z rating.
| Letter | Max Speed | Vehicle Types |
|---|---|---|
| L | 75 mph / 120 km/h | Off-Road Tires |
| M | 81 mph / 130 km/h | Temporary Spares |
| N | 87 mph / 140km/h | Winter Tires |
| P | 93 mph / 150 km/h | Winter Tires |
| Q | 99 mph / 160 km/h | Light Truck Tires |
| R | 106 mph / 170 km/h | Light Truck Tires |
| S | 112 mph / 180 km/h | Light Truck Tires |
| T | 118 mph / 190 km/h | Sedans |
| U | 124 mph / 200 km/h | Sedans |
| H | 130 mph / 210 km/h | Sports Cars |
| V | 149 mph / 240 km/h | Sports Cars |
| W | 168 mph / 270 km/h | Super Sports Cars |
| Y | 186 mph / 300 km/h | Super Sports Cars |