Are 315 Tires The Same As 33? | What The Numbers Mean

No, a 315 tire size names width, while a 33-inch tire names overall height, so they only line up in a few specific sizes.

A lot of truck and Jeep owners treat “315” and “33” like they mean the same thing. They don’t. That mix-up happens because both labels get used in the same garage talk, yet they describe two different parts of a tire.

A 315 tire starts with width. A 33-inch tire starts with total height. So when someone says “315s are 33s,” they’re usually rounding, skipping the aspect ratio, or talking about a common size they’ve seen before. That’s fine in casual talk. It’s not fine when you’re trying to buy the right tire, check clearance, or avoid rubbing.

The clean way to think about it is this: a 315 can be close to 33 inches tall, close to 34 inches tall, or even taller, depending on the full size printed on the sidewall. The rest of the code matters just as much as the 315.

Are 315 Tires The Same As 33? In Real Terms

No. “315” is the tire’s section width in millimeters. “33” is the tire’s overall diameter in inches. Those numbers don’t measure the same thing, so you can’t compare them as if they were equal.

Take a common size like LT315/70R17. That tire is about 34.4 inches tall on many spec sheets, not 33 inches. So a 315/70R17 is usually closer to a 34 than a true 33. On the other hand, a 315/60R20 lands much nearer to 34.9 inches. Same 315 width, different height.

That’s why the second number matters so much. In a metric tire size, the middle number is the aspect ratio. It tells you the sidewall height as a percentage of the width. Tire Rack’s sidewall size guide breaks that down clearly, and its tire dimension formula shows how width, aspect ratio, and wheel diameter work together to create the final height. Tire size markings on the sidewall are not just labels; they’re the whole math problem.

Why The Confusion Happens So Often

There are two naming systems at play. Metric sizes look like 315/70R17. Flotation sizes look like 33×12.50R17. One starts with width. The other starts with diameter. That alone causes a lot of crossed wires.

Then there’s rounding. People love shorthand. A tire that measures 33.2 inches may get called a 33. A tire that measures 34.4 inches may still get lumped into “about a 34.” Once that happens a few times in forums, shops, and group chats, the labels start to blur.

Marketing adds another wrinkle. A tire sold as a “33” may not measure exactly 33.00 inches once mounted, aired up, and carrying vehicle weight. Real specs vary by brand, tread design, wheel width, and load range.

What Each Number Actually Means

• 315 = section width in millimeters
• 70 = sidewall height as 70% of the width
• R = radial construction
• 17 = wheel diameter in inches
• 33 = overall tire diameter in inches in a flotation size

Once you split the numbers up that way, the question gets much easier. You’re not asking whether 315 equals 33. You’re asking whether one full tire size ends up near 33 inches tall.

315 Tire Size Vs 33-Inch Tire Size

Here’s where the answer gets practical. A 315-width tire can sit near a 33-inch tire in some cases, but it is not the same thing by default. The full code decides the outcome.

The quick math is simple: sidewall height equals width times aspect ratio, then doubled for top and bottom sidewalls, then the wheel diameter gets added. Tire Rack’s tire dimension method lays out that formula in plain terms. Tire dimension calculations make it easier to see why 315 alone tells only part of the story.

Tire Size	Approx. Overall Diameter	How It Compares To A 33
315/50R20	About 32.4″	Shorter than a true 33
315/55R20	About 33.6″	Close, a bit taller
315/60R18	About 32.9″	Very close to 33
315/60R20	About 34.9″	Well taller than 33
315/65R18	About 34.1″	Closer to 34
315/70R17	About 34.4″	Not a 33; closer to 34
33×12.50R17	Nominally 33.0″	Actual “33” flotation size
305/70R17	About 33.8″	Often near the “33” crowd

That table tells the whole story. Some 315 tires are near 33 inches. Some are not. So if your truck has room for a 33 but not a 34, choosing a random 315 is a gamble.

What Matters More Than The Name On The Sidewall

Fitment lives in the details. Width and height both change how a tire behaves on the vehicle. A wider tire can reach suspension parts sooner. A taller tire can catch the fender liner or pinch weld sooner. Two tires with near-matching diameters can still fit very differently if one is much wider.

Clearance

If you’re trying to avoid rubbing, overall diameter is only half the job. Section width, actual measured width, wheel offset, backspacing, and suspension travel all matter. A 315 tire is wide enough that even when its diameter looks workable on paper, the extra width may still create problems at full lock or full compression.

Gearing And Speedometer Change

A taller tire rolls farther with each turn. That can make your speedometer read low and soften acceleration. If you swap from a true 33 to a 34.4-inch 315/70R17, the jump is not tiny. You may feel it on hills, towing, or daily stop-and-go driving.

Wheel Choice

The wheel also changes the picture. A tire’s measured width can shift with wheel width. So even when two drivers both say they run 315s, one setup may sit wider or narrower than the other. That’s another reason not to buy by shorthand alone.

If You Want…	Check This First	Why It Matters
A true 33-inch height	Actual published diameter	315 alone won’t tell you height
No rubbing	Width, offset, and clearance points	Wide tires hit parts sooner
Stock-like gearing feel	New tire diameter vs stock	Taller tires change effective gearing
Good steering lock	Section width and wheel setup	Width affects turning clearance
An easy replacement	Load range and exact specs	Two “same size” tires can differ a lot

Which 315 Sizes Are Closest To A 33?

If your target is “about 33 inches tall,” some 315 sizes land much closer than others. A 315/60R18 is near that mark. A 315/55R20 also sits in the same neighborhood, though it runs a touch taller. Those are the sorts of sizes people may casually lump into “33-ish” territory.

A 315/70R17 does not belong in that camp. It usually lands in the mid-34-inch range. That means more clearance demands, a bigger hit to gearing, and a different look than a true 33.

When People Say “315s Are 33s”

Most of the time, they mean one of three things:

• They’re speaking loosely and not using exact measurements.
• They’re comparing one specific 315 size that sits near 33 inches.
• They’re repeating shop or forum shorthand.

That kind of shorthand is fine for conversation. It’s weak for buying parts.

How To Pick The Right Size Without Guessing

Start with the tire you have now. Look up its exact diameter and width. Then compare those numbers to the tire you want. Don’t stop at the first number in the size code. Read the full size, then check the published specs from the brand you plan to buy.

Next, think about what you care about most. If you want the look of a wider tire and still need to stay near 33 inches tall, some 315 sizes can work. If you just want a true 33, a flotation size or a narrower metric option may get you there with less fuss.

It also helps to be honest about your truck. A mild daily driver, a tow rig, and a trail build do not want the same thing from a tire. A width-heavy setup may look right but drive worse if it pushes past your wheel and suspension limits.

Final Verdict

315 tires are not the same as 33-inch tires. A 315 tells you width. A 33 tells you height. Some full 315 sizes end up close to 33 inches overall, though many do not.

If you’re shopping, skip the shorthand and check the full sidewall code plus the brand’s published specs. That one step can save you from rubbing, odd speedometer readings, and buying a tire that looks right on paper but fits wrong on the truck.