Tire Size Calculator & DOT Age

A tire size calculator, a tire size comparison and a DOT tire age checker in one app. Type the code molded on the sidewall and get plain numbers: diameter, load index, speed rating and the date the tire was made. Everything works offline.

TIRE SIZE CALCULATOR

Enter 225/45R17 and get overall diameter, section width, sidewall height, circumference and revolutions per mile and per kilometer. Metric, flotation (33x12.50R15) and old numeric (7.50-16) sizes are supported, so it doubles as a tire size converter from metric to inches. Every formula is shown on screen, so you can check the result yourself.

COMPARE TIRE SIZES

Compare two tire sizes, or up to four at once. See the diameter difference in percent, the speedometer error at real speeds, the change in ground clearance and width, and a clear verdict on whether the swap works. Find equivalent tire sizes for your rim, or go plus sizing with a bigger rim and the same rolling diameter.

SIDEWALL DECODER

Every marking explained in plain words: load index in kilograms and pounds, speed rating in km/h and mph, XL, Run Flat, M+S, 3PMSF snow tire symbol, Load Range and UTQG treadwear, traction and temperature grades.

DOT CODE AND TIRE AGE

Enter the DOT date code to get the week and year of manufacture, how old your tires are today, the plant that built the tire and a verdict based on tire manufacturer guidance.

TIRE AND WHEEL TOOLS

- Wheel offset calculator: compare wheel width, offset (ET) and spacers

- Tire pressure converter for PSI, bar and kPa, with temperature change

- Tread depth check and tread life estimate

- Bolt pattern (PCD) reference

- Load index needed from an axle weight

- Find the tire size from a target diameter

- Gear ratio after a tire size change

- Tire rotation patterns and a safety checklist

GARAGE AND HISTORY

Save your vehicles with their original tire size and compare a new tire in one tap. Saved tires, calculation history, print or save any result as PDF, and optional monthly and spring/autumn tire check reminders.

REFERENCE TABLES

Load index chart, speed rating chart, UTQG grades and where each marking sits on a sidewall, based on UNECE R30, 49 CFR 574 and the public NHTSA plant code dataset.

No account and no registration. Metric or imperial units, available in 15+ languages. Free, supported by ads.