ATV and UTV Tire Size Chart, Calculator and Conversions: How to Read and Compare Tire Sizes

An ATV or UTV tire size such as 25x8-12 lists three dimensions in inches: overall diameter (25 in), section width (8 in) and rim diameter (12 in). The dash means bias-ply construction. An R in that position, as in 25x8R12, means radial construction. A metric size such as 205/80R12 works differently. It gives section width in millimetres (205 mm), aspect ratio as a percentage (sidewall height is 80% of the width), construction (R for radial) and rim diameter in inches (12 in). With simple arithmetic you can convert one format to the other and compare sizes. The results are calculated nominal dimensions, not measured tire sizes and not a guarantee of fitment.

How to read ATV and UTV tire size markings

ATV and UTV tire size markings use one of two systems: inch sizing (diameter x width - rim) or metric sizing (width/aspect ratio, construction, rim). Both describe the same physical features in different units, so you need to know which system a tire uses before you compare it with another.

Inch format: 25x8-12 or 27x9R14

In inch format, the first number is the nominal overall diameter of the inflated tire. The second number is the nominal section width, and the last number is the rim diameter the tire must be mounted on. All three values are in inches.

• 25 in 25x8-12: overall diameter, about 25 in from tread to tread.
• 8: section width, about 8 in across the widest part of the tire, sidewall to sidewall.
• - or R: construction type. A dash indicates bias-ply and R indicates radial.
• 12: rim diameter in inches. The tire bead fits only a wheel of the same diameter.

Some tires write the width with decimals (25x8.00-12). This is the same nominal size as 25x8-12. Most UTV tire sizes use this inch format, for example 28x10R14, 30x10R14 and 32x10R15.

Metric format: 205/80R12

In metric format, the first number is section width in millimetres. The second number is the aspect ratio, which is sidewall height as a percentage of section width. The letter shows construction, and the last number is rim diameter in inches.

• 205: section width of 205 mm, about 8.07 in.
• 80: sidewall height equals 80% of 205 mm, which is 164 mm or about 6.46 in.
• R: radial construction. A dash in this position indicates bias-ply.
• 12: rim diameter of 12 in. Rim diameter is given in inches even in metric sizes.

Overall diameter is not printed in metric sizes. You calculate it from the other three numbers, as shown below.

Prefixes and position markings

Letters before the size identify the tire category, not a dimension. AT (as in AT25x8-12) usually stands for all-terrain and is common on ATV tires. Some tires also carry FRONT or REAR markings or a rotation arrow. These tell you where and in which direction the tire is designed to run. They do not change the size.

Which sidewall markings are dimensions and which are ratings?

Only the size code describes dimensions. Ply rating, load index, speed symbol and pressure figures describe performance limits or construction. A larger size number does not mean a stronger or faster tire, and a higher rating does not mean a larger tire.

Recommended inflation pressure comes from the vehicle manufacturer, not from the tire sidewall. On low-pressure ATV and UTV tires, pressure also affects the tire's actual dimensions.

ATV and UTV tire size chart

The chart below lists common ATV and UTV tire sizes. The values are calculated from the numbers printed on the tire. Sidewall height is (overall diameter − rim diameter) ÷ 2. Circumference is π × overall diameter. Revolutions per mile is 63,360 in ÷ circumference. The effective aspect ratio is sidewall height ÷ section width. Real tires can measure differently.

This chart works the same way whether you call it an ATV tire size chart, an atv tyre size chart or a utv tire size chart. Tires with the same overall diameter have the same calculated circumference, even when their width or rim size differs.

How to calculate tire dimensions: a manual ATV tire size calculator

An atv tire size calculator takes the numbers on the sidewall and returns sidewall height, overall diameter, circumference and revolutions per mile. You can do the same calculation by hand. The steps depend on whether the size is in inch or metric format.

Calculating an inch-format size

1. Read the overall diameter (D), section width (W) and rim diameter (R) in inches. For 26x9-12, D = 26, W = 9, R = 12.
2. Sidewall height = (D − R) ÷ 2. For 26x9-12: (26 − 12) ÷ 2 = 7 in.
3. Effective aspect ratio = sidewall height ÷ W × 100. For 26x9-12: 7 ÷ 9 × 100 ≈ 78%.
4. Circumference = π × D. For 26x9-12: 3.1416 × 26 ≈ 81.7 in.
5. Revolutions per mile = 63,360 ÷ circumference. For 26x9-12: 63,360 ÷ 81.7 ≈ 776.

Calculating a metric-format size

1. Read the section width in millimetres, the aspect ratio and the rim diameter in inches. For 205/80R12: 205 mm, 80%, 12 in.
2. Sidewall height (mm) = width × aspect ratio ÷ 100. For 205/80R12: 205 × 0.80 = 164 mm.
3. Convert the sidewall height to inches: 164 ÷ 25.4 ≈ 6.46 in.
4. Overall diameter = rim diameter + 2 × sidewall height: 12 + 2 × 6.46 ≈ 24.9 in.
5. Section width in inches = 205 ÷ 25.4 ≈ 8.07 in.
6. Circumference = π × 24.9 ≈ 78.3 in, which gives about 809 revolutions per mile.

These formulas assume an ideal, round, unloaded tire. They describe nominal geometry, not the measurements of a specific tire on a specific vehicle.

ATV tire size conversion: metric to inch and inch to metric

To convert between metric and inch sizing, convert millimetres to inches by dividing by 25.4, and inches to millimetres by multiplying by 25.4. You then derive the missing dimension. Metric sizes leave out overall diameter, and inch sizes leave out aspect ratio.

Converting metric to inch sizing

1. Calculate overall diameter as described in the metric steps above.
2. Convert section width to inches.
3. Write the result as diameter x width - rim (bias) or diameter x width R rim (radial).

Example: 205/80R12 calculates to about 24.9 x 8.07R12, so its nominal inch equivalent is roughly 25x8R12.

Converting inch to metric sizing

1. Section width in mm = width in inches × 25.4.
2. Sidewall height = (overall diameter − rim diameter) ÷ 2.
3. Aspect ratio = sidewall height ÷ width × 100.
4. Round to the nearest standard width and aspect ratio. The rounded figure is an approximation, not an exact match.

Example: 26x9-12 has a width of 9 × 25.4 ≈ 229 mm, a sidewall of 7 in and an aspect ratio of about 78%. The closest standard metric size, 225/80R12, calculates to about 26.2 in in diameter.

This atv tire size conversion chart and any UTV tire size conversion show nominal metric equivalents. A matching calculated size does not mean the two tires measure the same, or that a particular tire is made in that size.

UTV tire size comparison: how each number changes the tire

When you compare tire sizes, width, aspect ratio and rim diameter each affect sidewall height, overall diameter and circumference differently. The effect also depends on whether the size is written in inch or metric format.

Changing section width

In inch sizing, changing the width while keeping the same diameter and rim leaves the nominal sidewall height and overall diameter unchanged. Only the tire width and the effective aspect ratio change. 26x9-12 and 26x11-12 both have a calculated 7 in sidewall and a 26 in diameter. The 11 in tire is 2 in wider.

In metric sizing, aspect ratio is a percentage of width, so a wider tire with the same aspect ratio also has a taller sidewall. 205/80R12 has a 164 mm sidewall and a diameter of about 24.9 in. 225/80R12 has a 180 mm sidewall and a diameter of about 26.2 in.

Changing aspect ratio

In metric sizing, a lower aspect ratio means a shorter sidewall and a smaller overall diameter, as long as width and rim stay the same. 205/70R12 has a sidewall of 205 × 0.70 = 143.5 mm (about 5.65 in) and a diameter of about 23.3 in. That is roughly 1.6 in smaller than 205/80R12.

Changing rim diameter

A larger rim with the same overall diameter leaves less room for sidewall. 30x10R14 has a calculated 8 in sidewall, while 30x10R15 has 7.5 in. Both have the same nominal 30 in diameter and 94.2 in circumference. A tire must always match the rim diameter of its wheel exactly, so changing rim size also means changing wheels.

Worked UTV tire size comparison chart

To compare two sizes, calculate the dimensions of each one. Percent difference is (new − old) ÷ old × 100. The change in axle height is half the change in overall diameter.

Circumference determines how far the vehicle travels per wheel revolution. If the speedometer counts driveline or wheel rotations and is calibrated for 28x10R14 tires, it will read low by the same percentage with 30x10R14 tires. An indicated 30 mph becomes about 30 × 30 ÷ 28 ≈ 32.1 mph actual, based on nominal sizes. The extra ground clearance from a taller tire is only half the diameter increase, because the axle sits at the centre of the tire.

Nominal vs actual tire dimensions

Nominal dimensions are the figures printed in the size code. Actual dimensions are what a specific tire measures when it is mounted and inflated. They can differ noticeably, especially on low-pressure ATV and UTV tires.

• Manufacturer and tread design: tires with the same printed size from different makers, or with different tread patterns, can measure differently. Tall lugs often add diameter.
• Rim width: mounting on a wider or narrower wheel changes the measured section width.
• Inflation pressure: at the low pressures used on ATVs and UTVs, a small pressure change can noticeably change diameter and width.
• Load: the loaded radius from axle to ground is smaller than half the unloaded diameter.
• Wear: diameter decreases as the tread wears down.

Many manufacturers publish measured dimensions for each tire model. Those figures are more relevant than the nominal size when you compare specific tires.

How to measure actual tire size

1. Mount the tire on its wheel and inflate it to the pressure the vehicle manufacturer recommends.
2. To find overall diameter, lift the tire off the ground and measure tread to tread through the centre, or wrap a tape measure around the tread centreline to get the circumference.
3. If you measured circumference, divide it by 3.1416 to get diameter.
4. Measure section width across the widest point of the sidewalls, not across the tread alone.

Why calculated size does not guarantee fitment

Calculated geometry tells you how big a tire is in theory. It does not tell you whether that tire fits or suits a specific ATV or UTV. Fitment depends on the vehicle, the wheel and the actual tire, and none of these can be read from the size code alone.

• Rim diameter must match the wheel exactly. A 14 in tire mounts only on a 14 in wheel.
• Clearance: a larger diameter or width can contact fenders, suspension parts or frame components at full suspension compression or full steering lock, even if it clears at rest.
• Wheel offset and width change where the tire sits relative to the vehicle. These are wheel specifications, not tire size markings.
• Drivetrain effects: a larger circumference raises effective gearing and changes speedometer accuracy. On 4WD and AWD vehicles, the vehicle manufacturer's guidance on front-to-rear size combinations applies.
• Ratings: load index, ply rating and speed symbol should meet the vehicle's requirements, whatever the size.

For tire selection, use the vehicle manufacturer's specified sizes and the tire maker's published measurements alongside the calculated values. The calculations remain useful for understanding what the sidewall numbers mean and how large a dimensional difference really is.