Metric vs. Inch (Flotation) Tire Sizes: What's the Difference?

If you drive a standard sedan or a sports car, you're used to seeing tire sizes written like 225/45R17. This is the standard Metric sizing system.

But the moment you buy a Jeep, a truck, or start looking at off-road tires, you are suddenly hit with a completely different language: 33x12.50R15. This is the Inch sizing system (also known as Flotation sizes).

If you are trying to upgrade your truck's tires, looking at two completely different sizing systems can give you a headache. Let's translate this so it actually makes sense.

How to Read an Inch (Flotation) Tire Size

The Inch sizing system is actually incredibly straightforward and much easier to understand than the Metric system. It tells you exactly what you need to know in plain inches.

Let's look at 33x12.50R15:

• 33: This is the overall height (diameter) of the tire in inches. From the ground to the very top of the tire, it is 33 inches tall.
• 12.50: This is the width of the tire in inches. From sidewall to sidewall, it is 12.5 inches wide.
• R15: Just like the metric system, this means it is a Radial tire made to fit a 15-inch wheel.

That's it! No complicated percentages or aspect ratios to calculate.

How to Read a Metric Tire Size (A Quick Refresher)

The Metric system is a bit of a math equation.

Let's look at 285/70R17:

• 285: The width of the tire in millimeters.
• 70: The aspect ratio. The sidewall height is 70% of the 285mm width.
• R17: Fits a 17-inch wheel.

How to Convert Metric to Inches

A lot of truck owners want to buy "33-inch tires," but they are shopping for brands that only sell in Metric sizes. How do you know which Metric size equals 33 inches?

You have to do some math:

1. Divide the width (285) by 25.4 to get inches (11.22 inches wide).
2. Multiply the width by the aspect ratio percentage (285 * 0.70 = 199.5mm sidewall height).
3. Divide the sidewall by 25.4 to get inches (7.85 inches).
4. Multiply the sidewall by 2 (because there is top and bottom sidewall) and add the wheel diameter (17).
5. Total = 32.7 inches.

So, a 285/70R17 is essentially a 33-inch tire (32.7 inches).

The Easy Way Out

If doing geometry just to buy tires doesn't sound like a fun Friday night, don't worry. You don't have to do the math.

We built a tool that does the conversion instantly. Head over to our Metric to Inch Tire Conversion Calculator, type in your metric tire size, and we will instantly translate it into inches. You can also type in an inch size and we will give you the closest metric equivalents!