Tire tools and charts

Every calculator and chart on TireSizeCalc. Each one shows its working and lists its official sources.

Calculators

• Tire size calculatorCompare two sizes: diameter, width, speedometer and a to-scale drawing.
• Tire size converterMetric to inch sizes and inch to metric.
• Plus-size calculatorFind sizes that keep the diameter on a bigger or smaller wheel.
• Wheel offset calculatorBackspacing, poke and the space left at the suspension and fender.
• Re-gear calculatorEngine RPM and the axle ratio that restores it after a size change.
• Tire pressure light calculatorThe pressure at which the TPMS light must come on (FMVSS No. 138).
• Tread depth calculatorTread left to the 2/32 in wear bars, and the miles left.

Charts and reference

• Tire size chartEvery published size with its height and width in inches.
• Speed rating chartEach speed letter in mph and km/h.
• Load index chartLoad index 0 to 200 in pounds and kilograms.
• Load range chartC, D and E ply ratings with the FMVSS No. 138 pressures.
• Load range E tires10-ply rating, 80 psi maximum and the TPMS minimum.
• SL vs XL tiresStandard load and extra load tires compared.

For an explanation of the numbers on a tire, see the tire guides.

Printed from https://tiresizecalc.net/tools/. Figures as published on 2026-11-01. The sources are listed below.

Sources

1. 49 CFR 571.138 - Standard No. 138; Tire pressure monitoring systems. National Highway Traffic Safety Administration (NHTSA), Code of Federal Regulations, annual edition (GovInfo). 2022-10-01. S4.2(a) and Table 1: TPMS warning threshold. Retrieved 2026-11-01.
2. 49 CFR 571.139 - Standard No. 139; New pneumatic radial tires for light vehicles. National Highway Traffic Safety Administration (NHTSA), Code of Federal Regulations (eCFR). 49 CFR 571.139. eCFR up to date as of 2026-10-15. S5.4: treadwear indicators at 1/16 in (2/32 in). Retrieved 2026-11-01.
3. UN Regulation No. 30 - Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and their trailers (Revision 3). United Nations Economic Commission for Europe (UNECE). E/ECE/324 E/ECE/TRANS/505 Rev.1/Add.29/Rev.3. 2007-03-29. Para 6.1.2.1: sizing formula used by the size tools. Retrieved 2026-11-01.

Last reviewed 2026-11-01. The full source list, with dates and file checksums, is in How the numbers are calculated. To report an error, email contactus@tiresizecalc.net.