Updated May 2026 · Reviewed by NTW Tire Specialists
Tire Size Calculator: Metric to Inches
Quick version: a metric tire size like 285/75R17 doesn't tell you the height in inches — but it's easy to convert. Enter the width, aspect ratio, and rim diameter in the calculator below and we'll give you the real diameter and section width in inches, so you know how it compares to a 33″, 35″, or 37″ tire and whether it'll clear your truck.
Off-road tire sizes come two ways: metric (285/75R17) and high-flotation / inch (33x12.50R17). The inch sizes are easy — a 35 is about 35″ tall. Metric sizes hide the height in a formula. This calculator does that math for you, and the guide below explains how to read a size, what the common metric sizes work out to, and how going bigger affects fitment and your speedometer.
Metric Tire Size Calculator
Enter your tire's three numbers (from the sidewall, e.g. 285/75R17) and we'll convert it to inches.
How to Read a Tire Size
Take 285/75R17:
- 285 — section width in millimeters (the tread/sidewall width).
- 75 — the aspect ratio: sidewall height as a percentage of the width. Here the sidewall is 75% of 285 mm.
- R — radial construction (see our bias vs. radial guide).
- 17 — the rim diameter in inches the tire mounts to.
A high-flotation size like 33x12.50R17 reads simpler: 33″ overall diameter, 12.50″ section width, R radial, 17″ rim. Same tire, two languages — the calculator converts the metric one into these plain inches.
Common Metric Sizes, in Inches
| Metric size | Diameter | Roughly equals |
|---|---|---|
| 265/70R17 | ~31.6″ | 32″ tire |
| 285/70R17 | ~32.7″ | 33″ tire |
| 285/75R17 | ~33.8″ | 34″ tire |
| 315/70R17 | ~34.4″ | 35″ tire |
| 295/70R18 | ~34.3″ | 34″ tire |
| 35x12.50R17 | 35″ | 35″ tire (already in inches) |
These are nominal sizes — actual molded diameter varies a little by brand and tread. When clearance is tight, measure the real tire or call us.
Will a Bigger Tire Fit?
Going up a size adds height and width, and it's the width and the added diameter at full steering lock that usually rub first. As a rough guide: most trucks clear one size up on a level or small lift; 35s and up generally want a real lift and sometimes trimming. Bolt pattern and wheel offset matter too — see our bolt pattern guide — and bigger, heavier tires change your effective gearing and fuel economy. When in doubt, build it in our package builder or call and we'll spec it.
Frequently Asked Questions
How do I convert a metric tire size to inches?
Diameter (inches) = rim size + 2 × (width mm × aspect% ÷ 100) ÷ 25.4. For example, 285/75R17 = 17 + 2 × (285 × 0.75) ÷ 25.4 ≈ 33.8″. The calculator above does this for you — just enter the three numbers from the sidewall.
What size is a 285/75R17 in inches?
About 33.8″ tall and 11.2″ wide — commonly called a “34-inch” tire. It's one of the most popular off-road sizes on 17″ wheels.
What does a 35-inch tire convert to in metric?
The closest common metric equivalents are 315/70R17 (~34.4″) and 325/60R20 (~35.4″). A true 35x12.50R17 is already stated in inches, so no conversion is needed.
What is the aspect ratio in a tire size?
It's the sidewall height as a percentage of the section width. In 285/75R17, the “75” means the sidewall is 75% of 285 mm tall. A lower number (e.g., 285/55R20) means a shorter sidewall, which is why low-profile tires look the way they do.
Does a bigger tire affect my speedometer?
Yes. A taller tire travels farther per revolution, so your speedometer reads slower than you're actually going and your odometer under-counts miles. Our revolutions-per-mile chart shows the exact effect by size, and most trucks can be recalibrated to correct it.
How do I find my current tire size?
Read it off the sidewall — it's the string like 285/75R17 or 33x12.50R17 molded into the rubber. It's also on the placard inside the driver's door jamb (the factory size).
What's the difference between metric and high-flotation (inch) sizes?
They describe the same kind of tire in two formats. Metric (285/75R17) states width in millimeters and height as a ratio; high-flotation (33x12.50R17) states the overall diameter and width directly in inches. High-flotation sizes are common on aggressive off-road tires because the height is obvious at a glance.
Will changing tire size hurt my gas mileage?
Usually a little. Bigger, heavier tires take more energy to turn and change your effective gearing, so expect a small mpg drop going up a size or two — more with aggressive mud-terrains. See our all-terrain vs. mud-terrain guide for how tread type factors in.
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