A tire size chart in inches translates the metric code on a tire sidewall into measurements that are easier to compare: section width, sidewall height, and approximate overall diameter. For example, a 225/65R17 tire is about 8.9 inches wide, has a sidewall near 5.8 inches tall, and stands roughly 28.5 inches in diameter. Those figures are useful when comparing replacements, considering a different wheel size, or checking how much larger a tire may be. They are not a standalone fitment approval. The replacement must also suit the vehicle’s specified rim, load capacity, speed rating, suspension clearance, and recommended tire pressure.
Most passenger-car and light-truck tire sizes use a format such as 225/65R17. Each part supplies one part of the calculation:
The tire size chart in inches starts by converting millimeters to inches. One inch equals 25.4 millimeters. Divide the width by 25.4, then multiply the metric width by the aspect ratio to calculate sidewall height before converting that result to inches.
For a 225/65R17:
The diameter is approximate because sidewall markings describe nominal dimensions rather than a guaranteed measurement on every wheel. A tire mounted on a wider or narrower approved rim can measure differently from the same tire fitted to another rim width.
The following chart shows common metric sizes converted to inches. It is most useful for seeing relative differences between sizes, not for deciding fitment without checking the tire manufacturer’s specifications and the vehicle’s requirements.
| Metric tire size | Approx. width | Approx. sidewall | Wheel diameter | Approx. overall diameter |
|---|---|---|---|---|
| 195/65R15 | 7.68 in. | 4.99 in. | 15 in. | 24.98 in. |
| 205/55R16 | 8.07 in. | 4.44 in. | 16 in. | 24.88 in. |
| 215/60R16 | 8.46 in. | 5.08 in. | 16 in. | 26.16 in. |
| 225/65R17 | 8.86 in. | 5.76 in. | 17 in. | 28.52 in. |
| 235/65R18 | 9.25 in. | 6.01 in. | 18 in. | 30.02 in. |
| 265/70R17 | 10.43 in. | 7.30 in. | 17 in. | 31.61 in. |
A similar overall diameter does not mean two tires are interchangeable. The 195/65R15 and 205/55R16 examples are close in diameter, but they require different wheel diameters. A 16-inch tire cannot be installed on a 15-inch wheel, regardless of how close the outside diameter appears.
Section width is the tire’s nominal widest point from sidewall to sidewall, not necessarily the width of the tread that contacts the road. A wider tire can affect clearance around suspension parts, inner wheel wells, and fender edges. It may also require a different approved rim-width range.
Do not assume that moving from a 225 mm tire to a 235 mm tire adds exactly 10 mm of clearance demand in every direction. Tire shape varies by model, and wheel offset changes where the added width sits relative to the vehicle.
Sidewall height affects ride feel, wheel protection, and the tire’s overall diameter. A taller sidewall generally provides more cushioning over pavement joints and potholes, while a shorter sidewall usually leaves less flexible rubber between the wheel and the road.
Aspect ratio is not a fixed measurement. A 60-series tire does not always have the same sidewall height as another 60-series tire. A 225/60R17 has a taller sidewall than a 205/60R16 because 60 percent is being calculated from a wider tire.
Overall diameter is the figure most often used when comparing a stock size with a possible alternative. A larger diameter raises the vehicle slightly and travels farther per revolution. A smaller diameter lowers it slightly and turns more times over the same distance.
That change can affect speedometer and odometer readings, gearing behavior, clearance during turns and suspension movement, and the operation of vehicle systems that monitor wheel speed. The closer a replacement remains to the vehicle’s approved diameter range, the fewer secondary changes it is likely to introduce. Still, use the manufacturer-approved sizes rather than choosing solely by a calculated diameter difference.
Many all-terrain and off-road tires use an inch-based flotation format, such as 31x10.50R15. This is already expressed in inches:
A flotation size is convenient for broad comparisons, but it is still nominal. A tire labeled 31 inches may not measure exactly 31 inches once mounted and inflated. Check the tire maker’s published overall diameter, section width, approved wheel-width range, and revolutions-per-mile information when fitment is tight.
| Size format | Example | What it shows directly | What still needs checking |
|---|---|---|---|
| Metric passenger format | 225/65R17 | Width in mm, sidewall proportion, wheel diameter | Calculated outside diameter, approved rim width, load and speed ratings |
| Flotation format | 31x10.50R15 | Approximate outside diameter, width, wheel diameter | Actual mounted dimensions, approved rim width, load and speed ratings |
| Light-truck metric format | LT265/70R17 | Metric dimensions plus light-truck service designation | Load range, inflation requirements, vehicle suitability |
The letters before or after the size matter. A P-metric tire and an LT tire may have similar dimensional markings but different construction and load-service characteristics. Match the vehicle’s application and required load capacity rather than treating all same-size tires as equivalent.
Use a tire size chart in inches as one stage in a fitment check. Start with the tire placard, usually located on the driver-side door area, and the owner’s manual. These sources identify the original tire size, recommended cold inflation pressure, and sometimes approved alternative sizes.
To compare the size change, subtract the original calculated diameter from the replacement calculated diameter. To express the change as a percentage, divide that difference by the original diameter and multiply by 100.
For example, comparing 225/65R17 at approximately 28.52 inches with 235/65R18 at approximately 30.02 inches produces a difference of about 1.50 inches. The percentage difference is about 5.3 percent. That is a meaningful change in physical size, even before considering the wider section width and the different wheel required.
Diameter comparisons are especially useful for wheel-and-tire packages. Moving to a larger wheel can retain a similar overall diameter by using a shorter sidewall. For instance, the chart’s 195/65R15 and 205/55R16 examples are close in calculated diameter despite using different wheel diameters. That does not establish interchangeability, but it explains how larger wheels can be paired with lower-profile tires.
An inch conversion is particularly helpful if you are comparing two tires that use different metric widths or aspect ratios, deciding whether a wheel-size change preserves the approximate original diameter, or reading listings that use flotation sizing. It also gives a clearer sense of how much sidewall is being gained or lost before buying a replacement.
Choose an inch-based comparison as a screening tool when you are narrowing options. Avoid using it as the final approval for modified suspensions, non-stock wheel offsets, heavy towing use, or any setup with limited clearance. Those situations call for manufacturer specifications and, where needed, an experienced tire or vehicle-fitment professional.
Divide the width number by 25.4. For a 245 mm tire, 245 ÷ 25.4 equals approximately 9.65 inches. This is the nominal section width, and actual installed width can vary with wheel width and tire design.
Multiply the section width in millimeters by the aspect ratio expressed as a decimal, then divide by 25.4. For 225/65R17, multiply 225 by 0.65 and divide the result by 25.4. The sidewall height is approximately 5.76 inches.
No. The calculation produces an approximate nominal diameter based on the sidewall code. The actual measured diameter can differ by tire model, tread depth, wheel width, inflation pressure, and load, so use the manufacturer’s specification when clearance is close.
You can only use an 18-inch tire with an 18-inch wheel. A wheel-and-tire package may preserve a similar outside diameter by using a shorter sidewall, but the package must still meet clearance, load, brake-clearance, and vehicle fitment requirements.
Not necessarily. Tire compound, tread design, construction, inflation pressure, wheel width, weather conditions, and vehicle setup all affect handling. A wider tire can also create clearance issues or perform differently in standing water, snow, and rutted roads.
Usually, no. The vehicle tire placard provides the normal cold inflation pressure recommendation for the specified tire setup. A tire’s maximum pressure marking describes a limit associated with its load capacity, not a routine inflation target for every vehicle.
A tire size chart in inches makes the numbers on a tire sidewall easier to interpret: convert width, calculate sidewall height, and add the wheel diameter to find approximate overall height. Use those measurements to compare options and spot meaningful changes before buying. Then verify the complete replacement specification against the vehicle placard, owner’s manual, tire manufacturer data, and a qualified professional when fitment, load capacity, or clearance is uncertain.