Looking to buy new tires but you're not sure how the tire sizes change from metric to standard? Use this calculator to make sure you're getting the size you need!
How to Use This Tire Size Converter
Tire sizes in the US are labeled two different ways, and that can make shopping confusing. Most newer passenger cars, crossovers, and SUVs use metric sizing, which looks like 225/55R17 or 265/70R16. Older trucks, off-road tires, and some performance tires still use standard (imperial) sizing, which looks like 33x12.50R15 or 31x10.50R15.
Both formats describe the same physical dimensions. They just measure them differently. This calculator takes a metric size and converts it to the standard inch equivalent, so you can compare tires across both systems and confirm you're ordering the right size for your vehicle.
How Both Sizing Systems Work
A metric tire size has three parts. Take 265/70R17 as an example:
- 265 is the tire's width in millimeters, measured from sidewall to sidewall.
- 70 is the aspect ratio, which tells you the sidewall height as a percentage of the width. A 70 means the sidewall is 70% as tall as the tire is wide.
- 17 is the wheel diameter in inches.
Standard (inch) sizing works differently. Take 33x12.50R15 as an example:
- 33 is the overall tire diameter in inches, measured from the ground to the top of the tire when mounted.
- 12.50 is the section width in inches.
- 15 is the wheel diameter in inches.
Both formats describe the same physical tire. The converter calculates the inch equivalent from a metric input so you can compare them directly and confirm you're looking at the same size.
When This Calculator Is Useful
There are a few situations where knowing both measurements helps:
- You're replacing a tire and want to verify a metric size matches what was on your vehicle originally
- You're considering an upgrade and want to compare a standard-labeled tire to your current metric size
- You found a tire listing online that uses a different format than your vehicle's specification
- You're comparing prices across brands that label sizes differently
This converter gives you the overall diameter in inches, the section width in inches, and the sidewall height. Use those numbers to search for exactly what fits, or to verify that a tire you're considering is the right match.
Understanding the Result
After converting, you'll see the overall tire diameter, width, and sidewall height in inches. The diameter tells you how tall the tire is when mounted. The width tells you how wide it sits. Both matter for fit. A tire that's too tall can rub the fenders. A tire that's too wide can interfere with the suspension or inner wheel well.
Most passenger vehicles have some built-in tolerance, meaning a small range of sizes will fit safely. A change of plus or minus 3% in overall diameter is generally considered safe without any other modifications. Going beyond that range can affect your speedometer reading and how the vehicle handles.
If you're unsure whether a size is within a safe range for your specific vehicle, the percentage difference is a useful first check. Under 3% from your original size is almost always straightforward. Anything beyond that is worth confirming before you order.
Shopping After You Convert
Once you have your inch equivalent, use it as a reference when browsing. Only Tires carries tires in both metric and standard sizes across a wide range of brands and categories. If you know what metric size fits your vehicle but want to look at options labeled in inches, or the reverse, this tool bridges the gap.
After you run the conversion, use the Tire Size Comparison tool to see how your current size stacks up against an alternative before committing to a purchase.
Not sure what size is already on your vehicle? Check the sidewall of your current tire, or look at the sticker inside the driver's door jamb. That sticker lists the manufacturer's recommended size for your specific trim. Use that number as your starting point.
