Engine
Bore and stroke, compression, camshaft and airflow math.
How Gear Toolbox works
Every calculator on this site does one job and shows its working. Type your numbers and the result updates as you go: there is no submit button and nothing is sent anywhere. Next to the number you get a picture of it: a chart of engine speed in every gear, wheels and tires drawn to scale, or a time bar for a dragstrip pass.
My Garage is what ties them together. Save a build once, with its bore and stroke, compression, gear ratios, rear end, wheels and tires, and the calculators read the values they need when you open them. When a calculator works something out, such as the displacement of a stroker or the diameter of a new tire, you can save it back to the build after checking exactly what changes. Several builds can live side by side, and you can export them to a file or import them on another computer. It all stays in your browser; there is no account to create.
US units come first: inches, cubic inches, pounds, mph, psi and gallons. One switch on each calculator turns the inputs and results into metric, and the site remembers your choice.
What the calculators cover
Engine. Work out displacement from bore, stroke and cylinder count with the engine displacement calculator, or convert between cubic inches to liters and cc. Check static and dynamic compression before you pick pistons and head gaskets with the compression ratio calculator, and compare camshaft specs with the cam calculator. Piston speed, carburetor size and exhaust sizing round out the engine group.
Fuel. Size injectors from horsepower and brake-specific fuel consumption with the fuel injector calculator, check that the pump keeps up, convert between AFR and lambda, mix E85 with gasoline to a target blend and estimate the octane of a two-fuel mix. The gas mileage calculator handles mpg, L/100 km and the fuel cost of a trip at the price you enter.
Drivetrain. The gear ratio calculator shows engine speed in every gear at any road speed and compares rear gear and tire swaps; the rpm calculator focuses on cruise rpm and shift points; and the whp to hp calculator converts between wheel and crank horsepower.
Wheels and tires. See how far a new wheel moves in or out with the wheel offset calculator, check poke and inner clearance for a complete package, and compare two tire sizes drawn to scale with the tire size calculator.
Performance. Estimate elapsed time and trap speed from power and weight with the quarter mile calculator and its eighth-mile companion, get a 0-60 estimate, and size a turbocharger for a power target.
Where the numbers come from
Exact relationships, such as displacement, gear ratios or tire dimensions, are calculated exactly from the definitions behind them. Empirical formulas, like the classic quarter-mile estimates, are labeled as estimates on their pages, with where they come from and how far off they can be. Typical values, such as drivetrain loss or fuel consumption figures, come from technical references and are shown as ranges you can edit, because real engines vary.
Every result on this site is an estimate to plan a build with, not a promise of power or times. Measure your own parts, and confirm fitment and specifications with your shop or the parts manufacturer before buying or installing anything.