Tire Specifications
Select width, aspect ratio & rim size from dropdownsWidth
Select
Aspect %
Select
Rim (in)
Select
Select all three values
Calculated Specifications
Sidewall Cross Section
Revolutions Comparison
Tire Size Chart
| Tire Size | Overall Dia. | Width | Sidewall | Circumference | Revs/Mile | Revs/Km |
|---|---|---|---|---|---|---|
| Scroll down to load the tire size chart… | ||||||
For reference only. Always verify fitment with a professional before purchasing tires.
Need to convert tire sizes? Use our free Tire Size Converter for fast and accurate results.
How to Read a Tire Size
A tire size such as 265/70R17 looks like a code, but each part tells you something useful. The first number is the tire’s section width in millimeters, measured sidewall to sidewall. The second number is the aspect ratio — the sidewall height shown as a percentage of that width, so a lower number means a shorter, sportier sidewall. The letter R simply confirms the tire uses radial construction, which is standard on almost every tire sold today. The final number is the rim diameter in inches, and it must match your wheel exactly — this is the one measurement that has zero room for rounding. Once you know these four values, you can calculate the tire’s actual sidewall height, overall diameter, and circumference, which is exactly what the breakdown below does for you.
265
Section Width
Width in mm, sidewall to sidewall. 265 mm ≈ 10.4″
70
Aspect Ratio
Sidewall height as % of width. Lower = sportier.
R
Radial
Plies run radially at 90°. Standard on all modern tires.
17
Rim Diameter
Wheel size in inches. Must match exactly.
Sidewall = 185.5 mm
265 mm
×
70%
=
185.5 mm (7.3″)
Diameter = 752.1 mm (29.6″)
(185.5 × 2 ÷ 25.4)
+
17
=
29.6 inches
Circumference = 2362.4 mm (93.0″)
29.6″
×
π
=
93.0 inches
Looking for your tire size? Browse our Tire Size Chart.
Frequently Asked Questions
Common questions about tire sizes and specificationsWhat do the numbers on a tire size mean?
Tire size numbers follow a standard format like 265/70R17. The first number (265) is the tire width in millimeters. The second number (70) is the aspect ratio — the sidewall height as a percentage of the width. The letter R stands for radial construction. The last number (17) is the wheel rim diameter in inches. Together, these three numbers tell you exactly what size tire fits your vehicle.
How do I read my tire size correctly?
Look at the sidewall of your current tire — you will see a code that looks like P225/65R17 102T. Focus on the first three parts: 225 (width in mm), 65 (aspect ratio percentage), and 17 (rim diameter in inches). The “P” indicates a passenger tire, “102” is the load index, and “T” is the speed rating. For sizing purposes, you only need the width, aspect ratio, and rim size to use this tire size calculator.
Can I put bigger tires on my car or truck?
Yes, you can install bigger tires, but there are important limits to consider. A larger overall diameter changes your speedometer reading, odometer accuracy, gear ratio, and clearance inside the wheel well. Most experts recommend staying within 3% of the original tire diameter to avoid rubbing, ABS sensor issues, or transmission problems. Use this tire size calculator to compare your current size with a bigger option and see the exact diameter difference before buying.
How do I calculate tire diameter from size?
The tire diameter formula is: Diameter = (Width × Aspect Ratio × 2 ÷ 25.4) + Rim Diameter. For example, a 265/70R17 tire has a sidewall height of 265 × 0.70 = 185.5 mm. Multiply by 2 for both sidewalls = 371 mm. Convert to inches: 371 ÷ 25.4 = 14.61 inches. Add the 17-inch rim: 14.61 + 17 = 31.61 inches overall diameter. This calculator does all the math instantly — just select your size and hit Calculate.
Does changing tire size affect speedometer accuracy?
Yes, absolutely. Your speedometer is calibrated based on the original tire diameter from the factory. If you install a larger tire, it covers more ground per revolution, so your speedometer will read lower than your actual speed. For example, switching from a 30-inch to a 32-inch tire means when your speedometer shows 60 mph, you are actually traveling closer to 64 mph. Conversely, a smaller tire makes the speedometer read higher than actual. Always check the revolutions per mile difference using this calculator to understand the impact.
What is the most common tire size for SUVs and trucks?
The most common tire sizes for SUVs and trucks in the US are 265/70R17, 275/65R18, 275/60R20, and 285/70R17. The 265/70R17 is especially popular on vehicles like the Toyota Tacoma, Ford F-150, and Jeep Wrangler. For passenger cars, 205/55R16 and 225/65R17 are among the most widely used. You can browse the full tire size chart above to compare specifications across all popular sizes and find the best match for your vehicle.
What is tire aspect ratio and why does it matter?
The aspect ratio is the sidewall height expressed as a percentage of the tire width. A 265/70R17 tire has a sidewall height that is 70% of 265mm = 185.5mm. A lower aspect ratio (like 40 or 45) gives a shorter sidewall, which improves handling, steering response, and cornering stability — commonly found on sports cars and performance vehicles. A higher aspect ratio (like 70 or 75) provides a taller sidewall that absorbs bumps better, offering a smoother ride — typical on SUVs, trucks, and off-road vehicles. The aspect ratio directly affects the overall tire diameter, so changing it requires recalculating your specs.
What is the difference between tire width and tread width?
Tire width (the first number in the size, like 265) is the measurement from sidewall to sidewall when the tire is mounted and inflated — this is the section width. Tread width is the actual width of the rubber that contacts the road surface, which is always narrower than the section width. For example, a 265mm wide tire might have a tread width of only 220-240mm depending on the tire design, shoulder shape, and manufacturer. Two tires with the same size number can have different tread widths. This calculator uses section width for all calculations since that is the standardized measurement.
How many revolutions per mile should my tire have?
Typical passenger car tires range from 700 to 900 revolutions per mile. Smaller tires (like 205/55R16) revolve around 830-850 times per mile, while larger truck tires (like 285/70R17) revolve around 630-660 times per mile. The exact number depends on the overall diameter — a larger diameter means fewer revolutions because the tire covers more ground per turn. Your vehicle’s computer and speedometer are calibrated to a specific revs-per-mile number. If you change tire sizes, this number changes, which is why you should always compare revolutions per mile using this calculator before switching sizes.
What is tire sidewall height and how is it calculated?
Sidewall height is the vertical distance from the bead seat (where the tire sits on the rim) to the outer edge of the tread. It is calculated by multiplying the tire width by the aspect ratio percentage. For a 265/70R17 tire: 265mm × 0.70 = 185.5mm sidewall height (about 7.3 inches). The sidewall height appears twice in the overall diameter calculation — once on top and once on the bottom of the rim. A taller sidewall provides better cushioning and off-road performance, while a shorter sidewall gives sportier handling. This calculator shows the exact sidewall height in both millimeters and inches for any tire size you select.