What Is a 37 Inch Tire in Metric? | Size Numbers Made Clear

A 37-inch tire is about 940 mm tall, and its pure metric form is roughly 318/80R17 before rounding to real catalog sizes.

A 37-inch tire uses the flotation style you see on many truck and off-road tires, such as 37×12.50R17. That inch-based format tells you the overall diameter first, then the width, then the wheel size. Metric tires flip that logic. They start with width in millimeters, then show sidewall height as a percentage, then the rim size.

That’s why there isn’t one single metric twin for every 37-inch tire. You can convert the math cleanly, yet the size you can actually buy often gets rounded to a nearby width and aspect ratio. If you want the plain answer, a 37×12.50R17 works out to about 318/80R17 on paper, while 315/80R17 or 325/80R17 are the metric sizes people usually end up comparing in the real market.

What Is a 37 Inch Tire in Metric? The Actual Math

Start with the size many people mean when they say “37-inch tire”: 37×12.50R17. The three pieces are simple:

• 37 = overall tire diameter in inches
• 12.50 = section width in inches
• 17 = wheel diameter in inches

Now convert each inch value to millimeters. Since 1 inch equals 25.4 mm, a 37-inch tire is 939.8 mm tall. A 12.50-inch width becomes 317.5 mm. The 17-inch wheel becomes 431.8 mm.

Next, work out the sidewall height. Subtract the wheel diameter from the full tire diameter, then divide by two. That gives you 254 mm of sidewall height. Divide 254 by the 317.5 mm width and you get 0.80, or an 80-series sidewall.

So the clean metric translation is 318/80R17. That is the raw conversion. The catch is that tire makers sell widths in steps such as 315 mm, 325 mm, or 335 mm, not 318 mm. So the paper answer and the shelf answer don’t always match.

Why The Metric Match Is Often Approximate

Metric sizing and flotation sizing describe the same tire from different angles. Flotation sizes tell you the finished height right away. Metric sizes tell you width first, then sidewall proportion. Once you round to sizes that brands actually build, the final outside diameter can drift a little.

That small drift matters when you care about fender clearance, steering lock, speedometer error, gearing feel, or rubbing on the frame at full turn. A tire labeled 37 by one maker can sit a bit taller or shorter than a tire with the same label from another maker, especially once tread depth and load range enter the picture.

If you want a refresher on how metric sidewall codes are laid out, Goodyear’s how to read tire size page breaks down width, aspect ratio, and rim diameter. Yokohama’s sizing information page also shows that flotation light truck sizes use the inch format with the overall diameter first.

Size Piece	What The 37×12.50R17 Format Says	Metric Result
Overall diameter	37 inches tall from ground to top	939.8 mm
Section width	12.50 inches wide at the sidewall	317.5 mm
Wheel diameter	Fits a 17-inch wheel	431.8 mm
Sidewall height	(37 – 17) ÷ 2 = 10 inches	254 mm
Aspect ratio	Sidewall height relative to width	80%
Construction mark	R means radial	R stays the same
Pure metric expression	Direct math with no market rounding	318/80R17
Closest common shop sizes	Nearest buyable labels	315/80R17 or 325/80R17

37-Inch Tire In Metric Size Terms

Once you leave the calculator and start shopping, the conversation shifts from exact math to close fit. That’s where many buyers get tripped up. They search for a 37-inch tire in metric form and expect one clean answer, yet the better answer is “what wheel size, what width, and how close do you want to land?”

On a 17-inch wheel, 315/80R17 is one of the nearest metric sizes to a 37×12.50R17. It ends up a touch shorter than a labeled 37. A 325/80R17 lands a touch taller and wider. So one sits on the near side of the target, and the other leans just past it.

That’s why tire shops often ask a few extra questions before giving you a replacement size:

• Do you want to stay close to the original ride height?
• Is your current wheel 17, 18, or 20 inches?
• How much room do you have at full lock and full stuff?
• Are you matching the old tire’s width, or only its diameter?
• Do you need a certain load range for towing or extra cargo?

If your main goal is to match the outside height, a near-37 metric size can work well. If your goal is to match both height and width, you need to check the numbers more closely. Two tires can stand nearly the same height while one is much wider, and that changes rubbing risk, wheel offset needs, and road feel.

Common 37-Inch Conversions By Wheel Size

The wheel diameter changes the sidewall ratio. Keep the tire at 37 inches tall while moving from a 17-inch wheel to a 20-inch wheel, and the sidewall must get shorter. That changes the metric ratio even when the overall height stays near the same.

Flotation Size	Pure Metric Math	Closest Common Shop Talk
37×12.50R17	318/80R17	315/80R17 or 325/80R17
37×13.50R17	343/74R17	345/75R17
37×12.50R18	318/76R18	325/75R18
37×12.50R20	318/68R20	315/70R20
37×13.50R20	343/63R20	345/65R20

What Matters More Than The Label

A metric label that sits close to 37 inches still needs to fit your truck, wheel width, and use case. Clearance comes first. A wider tire may brush the sway bar, inner liner, or upper control arm even when the height looks fine on paper.

Load range also matters. A metric tire and a flotation tire that stand at nearly the same height may not carry the same weight at the same pressure. If your truck hauls tools, pulls a trailer, or carries a camper, the sidewall numbers matter as much as the diameter.

Then there’s speedometer change. A taller tire rolls farther in one turn, so the vehicle may show a lower road speed than the truck is actually doing. The bigger the jump from your stock tire, the more noticeable that gets. A gear change or recalibration may be worth it once you move into 37-inch territory.

What To Ask For At The Tire Shop

If you want clean answers fast, walk in with these numbers ready:

• Your current tire size
• Your wheel diameter and wheel width
• Your target height in inches
• Your target width in inches or millimeters
• Your truck’s lift, leveling kit, or stock ride height
• Your normal use: highway miles, towing, rocks, mud, or mixed driving

Say it like this: “I’m trying to match a 37×12.50R17. I want the closest metric size that keeps the height near 37 inches without going wider than I can clear.” That gives the shop enough detail to steer you toward the size that fits your truck, not just the size that looks close on a chart.

The Plain Answer

If someone asks what a 37-inch tire is in metric, the clean math answer is about 940 mm in diameter. For the common 37×12.50R17 size, the exact metric form is about 318/80R17. In real catalogs, the nearest metric choices are usually 315/80R17 or 325/80R17, with the better pick depending on your wheel, clearance, width target, and how tight you want the match to be.