How to Read Your Tire Size: What the Numbers on Your Sidewall Mean

If you've ever crouched down next to your car and stared at that string of numbers and letters on the side of your tire, you're not alone. In 25 years in the tire business, "what do all these numbers mean?" is one of the questions I get most. The good news: once someone shows you, you'll never be confused again — and you'll never get talked into the wrong tire because you couldn't read the right one.

Here's the whole code, in plain English.

Where to find your tire size

You don't have to guess. Your tire size is printed in a few easy-to-find places:

• The tire sidewall. Look for a sequence like 225/60R16 molded into the rubber. This is the actual size on the tire you're driving on right now.
• The driver's-door jamb sticker. Open your driver's door and look at the frame. There's usually a placard listing the manufacturer's recommended tire size and the correct inflation pressure.
• Your owner's manual. The tire and loading section spells out the original equipment size.

One quick tip: if the size on your sidewall doesn't match the door-jamb sticker, a previous owner may have changed sizes. When in doubt, the door-jamb placard is the size your vehicle was engineered for.

Decoding the size, number by number

A tire size like 225/60R16 reads as: 225 = tread width in millimeters, 60 = aspect ratio (sidewall height as a percentage of width), R = radial construction, and 16 = wheel diameter in inches. That's the entire code in one sentence — everything below is just the detail.

Width (the 3-digit number)

The first number is the section width — the distance across the tire from sidewall to sidewall, measured in millimeters. On our Lionhart LH-Ramani 225/60R16, that's 225 mm. A bigger number means a wider tire and a larger contact patch on the road. Going wider than your vehicle was designed for can affect handling, fuel economy, and whether the tire even clears your fenders — so it's not a number to change casually.

Aspect ratio (the 2-digit number)

The number after the slash is the aspect ratio, and it's a percentage, not a measurement. A "60" means the sidewall height is 60% of the tire's width. Lower numbers (like 45 or 50) mean a shorter, stiffer sidewall — sportier handling but a firmer ride. Higher numbers mean a taller sidewall that soaks up bumps and protects your wheel from potholes. On our Lexani 205/55R16, the 55 tells you the sidewall is 55% of 205 mm.

Construction letter (R = radial)

That single letter describes how the tire is built inside. R stands for radial, where the internal body plies run radially across the tire. Nearly every passenger tire sold today is a radial — it's the modern standard for ride quality and tread life. You may occasionally see a D (bias-ply, mostly on trailers and some specialty tires) or a ZR (a high-performance speed designation).

Wheel diameter

The last number in the size is the wheel (rim) diameter in inches — the size of the wheel the tire is built to fit. A 16 means it mounts on a 16-inch wheel. This one is non-negotiable: a 16-inch tire only fits a 16-inch wheel. It's also the fastest way to shop, which is why we group tires by wheel size — you can jump straight to 16-inch tires, 17-inch tires, and so on.

The load index and speed rating

Right after the size, you'll usually see something like 91V. Those two characters matter more than most people realize.

The load index (the number) tells you how much weight one tire can safely carry. A 91, for example, is rated for about 1,356 lbs per tire. It's a code, not the actual pounds, so it maps to a load chart — but the rule is simple: never go below the load index your vehicle calls for. This is especially important on trucks, SUVs, and heavier electric vehicles, which need a higher load rating than a small sedan.

The speed rating (the letter) is the maximum speed the tire is certified for over a sustained period. Common ones: T (118 mph), H (130 mph), V (149 mph). You don't need to drive anywhere near those speeds — the rating is also a rough indicator of how the tire handles heat and holds up under stress. Matching or exceeding your vehicle's original rating keeps handling and braking the way the engineers intended.

Other sidewall markings worth knowing

The size is the headline, but the sidewall has a few more things worth a glance:

• DOT date code. Look for "DOT" followed by characters ending in four digits — the last four are the week and year the tire was made. "2223" means the 22nd week of 2023. Tires age even when they're not driven, so this tells you how fresh a tire really is.
• UTQG / treadwear. You'll see "TREADWEAR," "TRACTION," and "TEMPERATURE" ratings. The treadwear number is a relative durability score — higher generally means longer expected tread life.
• M+S and the 3PMSF symbol. "M+S" (mud and snow) appears on most all-season tires. The three-peak mountain snowflake (3PMSF) is a stricter certification for real winter performance. If you deal with serious snow, that little snowflake matters — we break down exactly when in our guide on all-season vs. winter tires.

How to use your size to shop the right tire

Once you can read your sidewall, buying tires gets a lot less stressful. Jot down the full size and the load index and speed rating from your current tire (or your door-jamb sticker), and match it. Stay with the same size unless you have a specific, well-researched reason to change, and never drop below your vehicle's load index or speed rating.

From there it's about picking a tire that fits your driving and your budget — and you don't have to overpay to get a quality tire. If you're weighing names and price tags, our plain-English guide on what tire brands are worth it walks through the tiers honestly. And if you want your new tires to go the distance, the same habits we cover in 5 habits that make your tires last apply the day you put them on.

Written by Gaby, founder of TIRE OX. After 25 years in the tire and auto industry, I started TIRE OX to sell tires the honest way — and to teach drivers how to make them last.