How To Tell What Tire Size I Have | Read Sidewall Codes

Your tire size is printed on the sidewall and on the driver’s door placard, usually in a code like 225/45R17.

If you’ve ever stood next to your car staring at a tire and wondering what all those letters and numbers mean, you’re not alone. The good news is that your tire size is usually easy to find once you know where to look, and the code itself follows a pattern.

Most drivers can pin down the size in under two minutes. Start with the tire sidewall, then check the sticker on the driver’s door jamb. If those two don’t line up, the door placard and owner’s manual are the safer match for replacement tires on a stock vehicle.

How To Tell What Tire Size I Have On My Car

There are three places to check, and each one tells you something a little different.

Start With The Tire Sidewall

Look at the outer side of the tire. You’ll see a string such as P225/65R17 102H or 235/40R19 96V. That string is the size code plus load and speed details.

The size part is usually the easiest piece to spot because it stands out in larger molded lettering. On many tires, it sits near the brand name and model name. You may need to roll the car forward a little if the clearest section is near the ground.

Check The Driver’s Door Placard

Open the driver’s door and look for the sticker on the door jamb or door edge. This label lists the factory-recommended tire size and the cold tire pressure. If your car still has the original wheel setup, this sticker is often the most useful source when you’re buying replacements.

That sticker matters because a previous owner may have swapped the tires or wheels. Your sidewall shows what is mounted right now. The placard shows what the vehicle was built to use.

Use The Owner’s Manual If You Need A Tie Breaker

If the sidewall and placard leave you scratching your head, open the owner’s manual. It may list more than one approved size, especially on trims with larger wheels, sport packages, or optional tire sets for summer and winter driving.

That extra detail can save you from buying a size that fits the tire shop screen but doesn’t fit your trim, wheel width, or brake clearance.

What The Tire Code Means In Plain English

Once you find the code, the next step is reading it without turning it into homework. Let’s use P225/65R17 102H as a sample.

• P tells you the tire type. In this case, it’s a passenger tire.
• 225 is the tire width in millimeters.
• 65 is the aspect ratio, which means the sidewall height is 65% of the width.
• R means radial construction, which is what most road cars use.
• 17 is the wheel diameter in inches.
• 102 is the load index.
• H is the speed rating.

You do not need to memorize every letter on the tire. For day-to-day buying, the size itself, load index, and speed rating are the pieces that trip people up most often.

Prefix Letters And Small Add-Ons

You may see letters before or after the size. Those little tags carry extra meaning.

• P means passenger tire.
• LT means light truck tire.
• T usually marks a temporary spare.
• XL means extra load.
• M+S points to mud and snow use.

That’s why two tires that look close on paper may still not be a clean match. A 225/45R17 tire with a weak load rating is not the same thing as a 225/45R17 tire built for extra load.

Marking	What It Means	What To Watch
P	Passenger tire	Common on cars, crossovers, and many SUVs
LT	Light truck tire	Built for heavier duty use and different load needs
225	Tire width in millimeters	A wider tire may change clearance and ride feel
65	Aspect ratio	Smaller numbers mean a shorter sidewall
R	Radial construction	Standard on modern passenger vehicles
17	Wheel diameter in inches	Must match the wheel size exactly
102	Load index	Do not drop below the vehicle requirement
H	Speed rating	Match the vehicle spec unless a tire pro says otherwise
XL	Extra load construction	Often used on heavier cars and performance trims

If you want to see how manufacturers break down these sidewall markings, Michelin’s tire marking explainer lays out the same pattern in a clean visual format.

When The Sidewall And Placard Don’t Match

This is where people make expensive mistakes. If the tire on the car does not match the driver’s door placard, there are a few common reasons.

• The wheels were changed. A car may have aftermarket rims, so the current tire size is different from stock.
• The trim came with more than one setup. Some models have one size on base trims and another on sport trims.
• The car is wearing winter or spare tires. A winter package or temporary spare can throw off what you see at a glance.
• A previous owner guessed. It happens more than people think.

On a stock vehicle, the placard and manual should steer the call. The NHTSA tire safety page points drivers to the owner’s manual or the Tire and Loading Information Label on the driver’s side door edge or post when checking the correct tire size.

If your vehicle has been modified on purpose, use the current wheel size, tire clearance, and load needs before buying anything. That’s the point where guessing stops being cheap.

Where To Check	What You’ll Find	When It’s Most Useful
Tire sidewall	The size mounted on the car right now	Fast check when you’re standing by the vehicle
Door placard	Factory size and cold pressure	Best match for stock replacement tires
Owner’s manual	Approved sizes by trim or package	Useful when the sticker is missing or unclear
Spare tire label	Compact spare or temporary-use details	Handy when checking trunk or cargo-area spare gear

Tire Size Traps That Catch People

A tire size code looks neat and tidy, but there are a few traps hiding in plain sight.

Mixing Up Wheel Size And Tire Width

People often spot the “17” or “18” and think that’s the whole size. It isn’t. That number only tells you the wheel diameter. A 225/45R17 and a 245/65R17 both fit a 17-inch wheel, but they are not the same tire.

Ignoring Load Index And Speed Rating

Two tires can share the same width, aspect ratio, and wheel diameter but still be built for different loads and speeds. If your car calls for 102H and you buy a lower-rated tire, you’ve missed part of the fitment.

Reading The Spare And Assuming It Matches

Compact spares often have a narrow temporary-use size. If you check the spare by mistake, you can end up shopping for a tire that was never meant to stay on the car full time.

Trusting Only One Tire On The Car

If you bought the vehicle used, check more than one corner. Some cars end up with mismatched tires after a flat or a rushed replacement. One odd tire can send you down the wrong path.

Before You Buy New Tires

Once you know your size, do one last pass before you place the order.

1. Match the full size code. Width, aspect ratio, and wheel diameter all need to line up.
2. Check load index and speed rating. Stay at or above the vehicle requirement.
3. Check all four tires. Make sure one odd replacement isn’t fooling you.
4. Use the placard for a stock vehicle. It’s the cleaner call when the current tires look suspect.

If you’re still unsure, take a photo of the sidewall and the door placard before you shop. That gives you the current tire setup and the factory spec in one shot, which makes it easier to sort out a mismatch.

Once you know where the code lives and how to read each chunk, tire shopping gets a lot less messy. You’re not decoding random numbers anymore. You’re checking three plain facts: what is on the car, what the vehicle was built to use, and whether the replacement tire matches both.