How To Tell How Wide A Tire Is | Read The Size Code

A tire’s width is the first three-digit number in its sidewall size code, and you can confirm it by measuring sidewall to sidewall.

If you’re staring at a tire and the numbers look like alphabet soup, the width is still easy to spot once you know the pattern. On a tire marked 225/65R17, the “225” tells you the stated width in millimeters. That number refers to section width, which is the distance across the tire at its widest point from one sidewall to the other.

That last part trips people up. Many drivers look at the tread face, measure the rubber that touches the road, and get a smaller number. The sidewall code usually isn’t wrong. Tread width and tire width are not the same thing, so you need to know which one you’re checking.

How To Tell How Wide A Tire Is From The Sidewall

The fastest way is to read the sidewall code from left to right. Most passenger tires use a format close to this: P225/65R17 102H. You don’t need to decode every part to find the width. You just need the first three-digit number.

Here’s the easy version:

• P tells you the tire type for passenger vehicles.
• 225 is the tire width in millimeters.
• 65 is the aspect ratio, which compares sidewall height to width.
• R means radial construction.
• 17 is the wheel diameter in inches.

So if your tire says 205/55R16, the width is 205 mm. If it says 275/40R20, the width is 275 mm. No calculator needed for that first step.

What The Width Number Actually Means

The width number is a nominal measurement, not a promise that every mounted tire will measure that exact amount with a tape. A tire’s real-world width can shift a bit with rim width, inflation, and brand design. Still, the number on the sidewall is the standard starting point when you need to identify size, shop for replacements, or compare one setup with another.

Michelin’s page on tire sidewall markings uses the same reading order: the first three-digit number is the nominal section width in millimeters. That’s the piece you want when someone asks how wide the tire is.

Why Tread Width Can Look Smaller

The tread is the center band with the grooves. The sidewalls bulge past that band on many tires, so a tape laid across the tread often gives you a smaller reading than the size code. That doesn’t mean the tire was mislabeled. It just means you measured a different part of it.

Think of it this way: the sidewall number tells you the tire’s stated overall width at its widest area, while the tread tells you how wide the contact patch area is across the top. Both numbers matter, but they answer two different questions.

Where To Double-Check The Size On Your Car

If the sidewall is dirty, worn, or hard to read, check the driver-side door jamb. Most cars have a Tire and Loading Information label there with the factory tire size. NHTSA’s tire safety page says the label on the driver’s door edge or post and the owner’s manual are the places to check for the correct size on your vehicle.

This matters when your car has staggered sizes, aftermarket wheels, or a previous owner who swapped tires. The tire on the car might fit, but it may not be the original size. The door label tells you what the vehicle was meant to run.

Sidewall Part	What It Tells You	Example
P	Passenger tire type	P225/65R17
LT	Light truck tire type	LT265/70R17
225	Nominal section width in millimeters	225 mm wide
65	Sidewall height as a percent of width	65% of 225
R	Radial construction	R17
17	Wheel diameter in inches	17-inch wheel
102	Load index	Load rating code
H	Speed rating	Speed capability code

How To Measure Tire Width By Hand

If you want a real measurement instead of reading the code, use a tape measure. This is handy when the sidewall text is scuffed, the tire is off the car, or you’re checking whether a mounted tire runs wider or narrower than expected.

Measure The Widest Sidewall Point

1. Park on level ground and turn the wheel so the tire face is easy to reach.
2. Find the widest bulge on one sidewall.
3. Stretch the tape straight across to the widest bulge on the other sidewall.
4. Read the number in inches or millimeters.

This gives you the mounted width you can physically see. It may land close to the sidewall code, or it may vary a bit. That small gap is normal.

If You Want Inches

Many tire widths are printed in millimeters, but a lot of people think in inches. Divide the millimeter width by 25.4. A 225 mm tire is about 8.86 inches wide. A 265 mm tire is about 10.43 inches wide. You don’t need to be exact to the hundredth unless you’re matching wheel clearance on a tight setup.

Measure Tread Width Only When That’s Your Goal

If you’re checking snow-chain clearance, contact patch shape, or worn-edge patterns, you may want tread width instead. In that case, measure only across the tread face, not the sidewalls. Just don’t mix that number up with the official tire size.

What Usually Causes Confusion

Most mix-ups come from one of three spots: metric versus inch sizing, sidewall width versus tread width, and factory size versus what’s mounted now. Once you sort those out, the tire numbers stop looking mysterious.

• Metric code: 225/65R17 uses millimeters for width and inches for wheel diameter.
• Flotation code: 31×10.50R15 lists overall tire height first, then width in inches.
• Door label mismatch: the tire on the car may differ from the size listed by the vehicle maker.
• Brand-to-brand variation: two tires with the same code can measure a bit differently once mounted.

Flotation sizes are common on trucks and off-road builds. In 31×10.50R15, the “10.50” is the tire width in inches. That’s one case where the sidewall gives you the width without a metric conversion.

Marked Width	Approx. Inches	What You’re Reading
195 mm	7.68 in	Narrow passenger tire width
205 mm	8.07 in	Common compact or midsize width
225 mm	8.86 in	Common sedan or crossover width
245 mm	9.65 in	Wider sport or SUV fitment
265 mm	10.43 in	Common truck or performance width
10.50 in	10.50 in	Flotation size already shown in inches

When The Width Number Matters Most

You don’t need the tire width just to satisfy curiosity. Width affects wheel fit, fender clearance, steering feel, wet-road behavior, and whether a replacement tire matches the car’s original setup. It also changes the sidewall height when the aspect ratio stays the same.

Say you move from a 225/45R17 to a 245/45R17. The width grows by 20 mm, and the sidewall height grows too because 45 percent of 245 is taller than 45 percent of 225. That can change clearance and speedometer reading, even though the wheel diameter number stayed the same.

Use The Placard Before You Buy

If you’re shopping for new tires, start with the placard and the owner’s manual, then compare that size with the sidewall on the current tire. If both match, you’re set. If they don’t, figure out whether the car was intentionally changed to a different fitment or whether the wrong size was installed at some point.

A clean tire-size check takes less than a minute. Read the first three-digit number on the sidewall for section width, measure sidewall to sidewall if you want a physical check, and use the door-jamb label to confirm what belongs on the car. That’s the whole play.