What Size Is A 37 Inch Tire In Metric? | Closest Metric Pick

A 37-inch tire usually lands closest to 315/80R17, though the true metric match shifts with width and wheel size.

A 37-inch tire sounds simple until you try to buy one in metric sizing. That’s where the mix-up starts. “37-inch” is a flotation size. It tells you the tire’s rough overall diameter in inches, and it often travels with a width and wheel size, such as 37×12.50R17. Metric sizing uses a different format, like 315/80R17, and that format builds the tire from three parts: width in millimeters, sidewall height as a percentage, and wheel diameter in inches.

So if you’re trying to swap a 37-inch tire into a metric size, there is no single one-line answer for every setup. The closest match depends on the wheel diameter you’re running, how wide you want the tire to sit, and how much real-world diameter change you can live with. Get that part wrong and the truck can feel a bit off. Gearing, speedometer reading, fender clearance, and steering lock all come into play.

Why A 37-Inch Tire Does Not Have One Metric Twin

A flotation size bakes the overall diameter right into the name. A metric size does not. With metric tires, you have to calculate overall diameter from the sidewall and the wheel. That means two metric tires can have close diameters but wear different widths, or they can match width and still miss the height.

Goodyear’s sidewall size breakdown lays out the pieces: section width, aspect ratio, and rim diameter. Once you know those three numbers, you can compare a metric tire with a flotation tire instead of guessing from the name alone.

The Math Behind The Swap

The basic formula is short:

• Overall diameter = wheel diameter + twice the sidewall height
• Sidewall height = section width × aspect ratio
• Since width is in millimeters, divide by 25.4 to turn it into inches

Take 315/80R17. The width is 315 mm, which is about 12.4 inches. The sidewall height is 80 percent of 315 mm. Run that math, add the 17-inch wheel, and you land at about 36.8 inches overall. That’s why 315/80R17 gets named so often as the closest metric stand-in for a 37×12.50R17.

What Size Is A 37 Inch Tire In Metric On A 17-Inch Wheel?

On a 17-inch wheel, the most common answer is 315/80R17. It lands close on both height and width, which is why it shows up again and again on trucks that want a metric version of a 37×12.50R17. There are other near matches, yet they change the shape in ways you may or may not want.

Toyo’s 17-inch, 37-inch tire search shows real flotation sizes in this range with listed diameters around 36.8 inches, which is a good reminder that a “37” on the sidewall is often a rounded label, not a dead-on lab number. That small gap is normal across brands and tread designs.

If your target is the classic 37×12.50R17 look, 315/80R17 is the cleanest metric match for most people. If you want more width, you start drifting into sizes that can be taller, heavier, or both. If you want a tighter fit, you can step down into a metric size that sits a little under 37 inches and trims rubbing risk.

Metric Size	Approx. Diameter / Width	What It Means On A Truck
315/75R17	35.6 in / 12.4 in	Close in width, shorter than a true 37, easier fit on many builds
315/80R17	36.8 in / 12.4 in	Closest all-around swap for a 37×12.50R17
325/80R17	37.5 in / 12.8 in	A touch taller and wider, can crowd gears and clearance
335/80R17	38.1 in / 13.2 in	Pushes past 37, better only if you want extra height
345/70R17	36.0 in / 13.6 in	Wide stance, shorter height, fills the wheelwell sideways more than upward
325/85R16	37.8 in / 12.8 in	Near-37 option for 16-inch wheels, taller than 315/80R17
355/65R18	36.2 in / 14.0 in	Wide 18-inch choice, closer in height than many expect
285/90R17	37.2 in / 11.2 in	Tall and narrow, better for a pizza-cutter style build

How Width, Wheel Size, And Real Clearance Change The Answer

Here’s the part many size charts skip. A 37-inch tire is not just a height number. Width changes how the truck behaves and where the tire hits first. A narrow 37-ish metric tire may clear the upper control arm and the pinch weld more easily. A wide one can crowd both, even when the diameter looks close on paper.

Wheel size changes the sidewall shape too. A 37-inch tire on a 17-inch wheel has more sidewall than a near-37 tire on an 18-inch or 20-inch wheel. More sidewall usually means a softer ride and more flex off-road. Less sidewall sharpens the look and road feel, though it also leaves less cushion when you air down.

Three Checks Before You Buy

1. Match the wheel diameter first. A 315/80R17 only works on a 17-inch wheel, not an 18 or 20.
2. Match the width second. If you’re replacing a 12.50-inch tire, a 315 mm section width is usually close.
3. Check measured specs from the tire brand, not just the molded size name.

Brand Measurements Matter

That last point saves headaches. One brand’s 315/80R17 may stand slightly taller or wider than another brand’s tire with the same printed size. The difference may look small on paper, yet it can be enough to change rubbing at full lock or full stuff.

Closest Metric Matches For Common 37-Inch Setups

If you already know the wheel size and the look you want, the swap gets easier. The table below keeps it practical. These pairings are not the only choices on the market, though they are the ones most buyers start with when they want a metric size that feels close to a 37-inch flotation tire.

Flotation Size	Closest Metric Match	Fit Note
37×12.50R17	315/80R17	Closest blend of height and width for the classic setup
37×13.50R17	345/75R17	Near-perfect width match, with height sitting a hair over 37
37×12.50R18	325/75R18	Close in diameter, a touch wider than a 12.50 tire
37×13.50R18	345/70R18	Strong match when you want width without jumping to a taller tire
37×12.50R20	355/60R20	Close in height, wider than stock for many trucks

When The Closest Metric Size Is Not The Best One

The closest metric number is not always the smartest buy. If your truck already rubs a little with its current tires, dropping to a 35.6-inch 315/75R17 may fit better than forcing a true near-37 size. If the truck feels lazy off the line, a slightly shorter tire can help bring some snap back without touching the gears.

Load rating matters too. Many 37-inch and near-37 metric tires are built for heavy-duty use, and that can add weight and stiffness. On a daily-driven truck, that extra mass can change braking feel, ride quality, and fuel use. On a trail build, the same traits may be worth it if the casing is tougher and the tire holds up better at low pressure.

A Good Rule Of Thumb

• Want the classic 37×12.50R17 swap? Start with 315/80R17.
• Want a little more room under the truck? Try 325/80R17 or 325/75R18, depending on wheel size.
• Want less rubbing and easier street manners? Stay just under 37 inches.
• Want a narrow, tall setup for mud or snow? 285/90R17 can make sense.

Picking The Right Metric Size Without Regret

If you want the plain answer, a 37-inch tire is usually closest to 315/80R17 in metric form, especially when people mean a 37×12.50R17. Still, that answer works best only when the wheel size, width target, and measured specs line up with your truck. That’s why the smartest move is to treat “37-inch” as a starting point, then match the tire by actual diameter, width, and brand spec sheet.

Do that, and the swap feels a lot less muddy. You get a tire that looks right, fits better, and behaves the way you expect when the truck finally rolls out of the shop.