Free · no sign-up · works on your phone

Car math, done in seconds.

Compare tire sizes before you buy, check how much you can tow, decode a VIN, and work out what a trip costs in gas.

Tires & wheels

Tire size calculator Compare two tire sizes: diameter, width, sidewall and speedometer error.

Tire size chart Diameter in inches and revolutions per mile for common tire sizes.

Tire size decoder What every part of a tire code means, from width to load index and speed rating.

Fuel & trips

Gas calculator What a drive costs in gas, one way or round trip, split between riders.

MPG calculator Your real gas mileage from a fill-up, with L/100 km and cost per mile.

Towing & vehicle

Towing capacity calculator How heavy a trailer you can really tow, from your ratings and payload.

VIN decoder Look up any VIN: year, make, model, engine and where it was built.

Battery group size chart Car battery sizes and dimensions, and how to find the one that fits.

Before you buy new tires

Changing tire size changes more than the look. A taller tire makes the speedometer read low and can rub; a lower profile rides firmer. The tire size calculator shows the difference in diameter and speed, and lists sizes within the safe 3% range. The tire size chart gives the diameter in inches of common sizes at a glance.

Before a road trip

The gas calculator turns distance, MPG and gas price into a trip cost you can split with friends, and the MPG calculator tells you what your car really gets from a fill-up.

Before you tow or buy

A truck’s advertised towing capacity is for one ideal configuration. The towing capacity calculator works out what yours can really pull once passengers, cargo and tongue weight are counted. Looking at a used car? The VIN decoder shows the year, engine and plant it was built in, and the battery group size chart tells you which replacement battery fits.

Questions

Are these car calculators free?

Yes. Every calculator is free with no sign-up. The site is supported by ads, which never sit inside a calculator.

How accurate are the results?

Tire figures are calculated from the size code with the standard formulas, so they match published specs to a few hundredths of an inch; real tires vary slightly by brand. Fuel results are only as accurate as the MPG and price you enter.

Do they work on my phone?

Yes. Every calculator works on phones, tablets and computers, and updates as you type.