Tire dimensions: how they’re measured and how to use them to find the right size

Tire dimensions tell you the size and shape of a tire so you can confirm fitment, calculate clearances, and choose the right replacement. You’ll see these measurements on your tire’s sidewall and in spec sheets, expressed in millimeters, inches, and percentages.

If you already know your vehicle, skip the math and let our tools do the work: - Use the tire size conversion calculator to compare sizes and check speedometer and clearance changes. Open the tire size calculator. - Prefer a guided shopping experience? Enter your vehicle and driving style, and Treadwell will match tires that fit. Find tires with Treadwell.

How to read your tire size

Most tires use one of three formats printed on the sidewall.

• P-metric (passenger) example: 225/65R17 102H
• 225: section width in millimeters
• 65: aspect ratio (section height is 65% of section width)
• R: radial construction
• 17: rim diameter in inches

• 102H: load index and speed rating

• LT-metric (light truck) example: LT275/70R18

• Same structure as P-metric, optimized for higher load capacity.

• Flotation (inch-based) example: 35x12.50R17LT

• 35: overall diameter in inches
• 12.50: section width in inches
• 17: rim diameter in inches
• LT: light truck construction

Note: Actual, measured dimensions vary slightly by brand/model, inflation pressure, and the wheel width the tire is mounted on. Always confirm specs in the product details or with our team.

Key tire measurements explained

• Section width
• The width from the widest point of the outer sidewall to the widest point of the inner sidewall (not just the tread). First number in a metric size (e.g., 225 in 225/65R17).
• Overall width
• Sidewall-to-sidewall width including any raised features like rim protectors or whitewalls.
• Tread width
• The width of the tread surface that contacts the road.
• Rim width
• The approved range of wheel widths a tire can be mounted on. Mounting on wider/narrower wheels changes measured section width slightly.
• Section height
• The distance from bead (where the tire seats on the wheel) to the top of the tread. Calculated from aspect ratio: section height = section width × aspect ratio.
• Overall diameter
• The outside diameter through the center of the tire, measured inflated with no load.
• Rim diameter
• The diameter of the wheel at the bead seat area across the wheel (in inches). This must match the tire’s rim diameter.
• Circumference
• The distance around the outside of the tire. Used to calculate revolutions per mile.

Handy formulas and quick checks

• Section height (mm) = section width (mm) × aspect ratio
• Overall diameter (in) ≈ [2 × section height (mm) ÷ 25.4] + rim diameter (in)
• Circumference (in) ≈ overall diameter (in) × 3.1416
• Revolutions per mile ≈ 63,360 ÷ circumference (in)

Example (225/50R17): - Section height = 225 × 0.50 = 112.5 mm - Overall diameter ≈ (2 × 112.5 ÷ 25.4) + 17 ≈ 25.9 in

Use the calculator to quickly compare any two sizes and see speedometer impact and clearance changes. Try the tire size calculator.

Using these measurements to choose the right size

• Match rim diameter exactly. A 17-inch tire mounts only on a 17-inch wheel.
• Keep overall diameter close to stock (commonly within about 3%) unless your vehicle is modified for larger tires.
• Confirm width and sidewall bulge clear brakes, fenders, and suspension at full lock and full compression.
• Maintain or exceed your original load index and choose an appropriate speed rating.

For an easy, vehicle-specific path, Treadwell handles these checks automatically. Find tires with Treadwell.

Answers to common questions

• Where can I find 35-inch tires?

• Look for flotation sizes like 35x12.50R17 or 35x12.50R20. Enter your vehicle in Treadwell to see 35-inch options that fit, or visit a nearby store to verify clearance and wheel specs. Find tires with Treadwell or find a store near you.

• Where is the tire manufacture date located?

• On the DOT code stamped into the sidewall. The last four digits show the week and year of manufacture. Example: DOT … 2319 = 23rd week of 2019. The full DOT code may appear on only one side of the tire.

• What services do tire centers typically include with purchase?

• Professional mounting and balancing
• New rubber valve stems or TPMS service kits as needed
• Old tire disposal

• Complimentary rotation, rebalancing, flat repair, and air-pressure checks for the life of the tires are commonly included by many shops. Road-hazard coverage may be available as an add-on. Ask your local store for details.

• Where can I find car tires near me?

• Enter your ZIP to see nearby locations, real-time inventory, and book installation. Find a store.

• Where can I find all-season tires near me?

• Browse all-season options and enter your vehicle to ensure a perfect fit. Shop all-season tires.

Ready to go? You can buy online and book your install in minutes. Make an appointment.