Enter a tire size

Use the printed-size input

Enter a size such as 225/45R18. Optional P or LT prefixes, R or ZR, lowercase letters and spaces between the parts are accepted. For example, LT265/75 R16 and 245/40ZR18 supply the three geometric dimensions. Read back width, aspect ratio and rim diameter before using the result; a typing error can still produce a different valid size.

The normalized display identifies geometry only. It does not make an LT marking equivalent to a passenger designation or interpret ZR as a complete speed rating. Keep the exact product marking and service description separately when comparing real tires.

Use manual fields for explicit dimensions

Switch to manual entry to provide width in millimeters, aspect ratio in percent and rim diameter in inches separately. Width accepts 50–600 mm, aspect ratio 10–100 percent and rim diameter 5–30 inches, including the endpoints. These bounds describe the calculator’s supported inputs, not a catalog of manufactured sizes.

Decimal inputs use a decimal point, such as 17.5. Grouping commas and exponent notation are rejected. Empty, non-finite and out-of-range values cannot produce a result. A manual dimension is a calculation input, not evidence of an available tire.

Do not guess what an extra suffix means

A complete service description may contain extra load or speed information. Unknown suffixes such as the 95W in “225/45R18 95W” are rejected instead of silently discarded. Enter the supported size portion for geometry, then retain the complete service description in your own product notes. The calculator does not evaluate load index or speed rating.

Correct the field that needs attention

An error message identifies the invalid field while keeping your typed text available. Correct that field and calculate again. Do not interpret a previous valid result as a result for the rejected input. The default example is available if you want to restart with a known, complete comparison.

Use the directory as a separate reference

Directory entries have manufacturer-source records for their markings. The calculator can work with supported values outside that directory, but it does not certify that every mathematically valid combination is manufactured or appropriate for a vehicle.

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