Tire Conversion Calculator

In a metric tire size like 265/70R17, the first number (265) is the tire width in millimeters. The second number (70) is the aspect ratio, which tells you the sidewall height as a percentage of the width. The letter R means radial. The last number (17) is the wheel diameter in inches. In an inch size like 33X12.5R17, the first number (33) is the total tire height in inches, the second number (12.5) is the tire width in inches, and the last number (17) is the wheel diameter in inches.

Yes. You can paste a full tire size like 265/70R17 or 33X12.5R17 into the first input field. The calculator will detect the format, switch to the correct mode, and fill in all three fields for you automatically.

Enter your metric tire size in the calculator using the Metric input format. The tool will show the inch equivalent in the Equivalent Size section. For example, a 265/70R17 is close to a 31.5X10.5R17 in inch format. The calculator does all the unit conversion math for you.

Switch the input format to Inch, then type in the overall height, section width, and rim diameter. The calculator will display the closest metric equivalent. For example, a 33X12.5R17 is close to a 315/70R17 in metric format.

For a metric tire, the formula is: Overall Diameter = (Rim Diameter × 25.4) + (2 × Sidewall Height). The sidewall height equals the section width times the aspect ratio divided by 100. Everything is converted to the same unit before adding. The calculator shows this math in the Step-by-Step Solution section.

Revolutions per mile tells you how many times a tire rotates to travel one mile. A smaller tire spins more times per mile, and a larger tire spins fewer times. This number affects your speedometer accuracy, odometer readings, and fuel economy. The calculator finds it by dividing 63,360 (inches in a mile) by the tire's circumference in inches.

Most experts recommend staying within 3% of your original tire's overall diameter. Going beyond 3% can cause noticeable speedometer error, affect your braking distance, and put extra stress on your drivetrain. The comparison tab shows the exact percentage difference between two tire sizes so you can check this easily.

A bigger tire covers more ground per rotation. Your speedometer thinks each rotation is the same distance as the original tire, so it reads lower than your actual speed. For example, if your speedometer says 60 mph, you might really be going 62 mph. The comparison tab includes a speedometer correction chart that shows the exact difference at various speeds.

A smaller tire covers less ground per rotation, so your speedometer reads higher than your actual speed. If your speedometer says 60 mph, you might really be going 58 mph. Your odometer will also add miles faster than you actually drive.

The speedometer correction chart shows your actual speed when your speedometer displays a certain reading. It is calibrated for your original tire (Tire 1). If you install a different tire (Tire 2), the chart tells you whether you are going faster or slower than the dashboard shows. Readings off by more than 3 mph are highlighted as warnings.

This table estimates your engine RPM at 65 mph for different axle gear ratios when using the new tire. Lower gear ratios with a larger tire will reduce RPM, which can improve fuel economy. Higher gear ratios with a smaller tire will raise RPM, which gives more power but uses more fuel. The table marks each ratio as fuel economy, factory, or performance zone.

This feature finds tire sizes that fit a new wheel diameter while keeping an overall diameter close to your current tire. Enter a new rim size (like 20 inches), and the calculator lists up to 8 compatible tire sizes within 1.5 inches of your original tire's diameter. This is useful when upgrading to larger wheels or downsizing for winter.

The alternate tire sizes table lists common tire sizes that are within 1 inch of your current tire's overall diameter. Each row shows the metric size, inch size, overall diameter, and the difference from your original tire. You can filter the list by rim diameter to narrow down the options.

Aspect ratio is the height of the tire's sidewall expressed as a percentage of its width. A tire with a 70 aspect ratio has a sidewall that is 70% as tall as the tire is wide. A lower aspect ratio means a shorter, stiffer sidewall. A higher aspect ratio means a taller, more cushioned sidewall.

Section width is the measurement of the tire from one sidewall to the other at its widest point, not counting any raised lettering or trim. In metric tire sizes, it is given in millimeters. For example, in 265/70R17, the section width is 265 mm (about 10.4 inches).

Sidewall height is the distance from the wheel rim to the outer edge of the tread. It is calculated by multiplying the section width by the aspect ratio. A taller sidewall gives a softer ride and better protection against potholes. A shorter sidewall gives sharper handling and a sportier look but a firmer ride.

Yes. The calculator works with any passenger, truck, SUV, or off-road tire size. Just switch to Inch mode if your tire uses the inch format common on off-road tires (like 35X12.5R17), or stay in Metric mode for standard sizes. The math is the same for all radial tires.

In the comparison visualizer, blue/purple represents Tire 1 (your original tire) and orange represents Tire 2 (your new tire). You can view them side by side or overlaid on top of each other to see the size difference clearly.

It depends on your vehicle manufacturer and how far you deviate from the factory tire size. Small changes (within 3% of the original diameter) usually do not cause issues. Large changes can affect safety systems like ABS and traction control, which could give a dealer reason to deny a warranty claim related to the drivetrain. Always check your owner's manual or ask your dealer before making big changes.

If your new tire's overall diameter is more than 3% different from the original, you should recalibrate your speedometer. Many modern vehicles allow a dealer to reprogram the ECU for the new tire size. Aftermarket speedometer calibrators are also available. The comparison tab's speedometer chart shows exactly how far off your readings will be, so you can decide if a recalibration is needed.

No. This calculator uses the standard tire size numbers printed on the sidewall. Actual measurements can vary slightly between tire brands and models. Tread depth also changes as the tire wears, which slightly reduces the overall diameter over time. The calculated values represent the tire at its nominal, new size.

Yes. Click the Print Results button to open your browser's print dialog. You can print the page or save it as a PDF. The input controls are hidden in the printout so you get a clean summary of your tire specs, comparison charts, and diagrams.