Your car engine is a heat engine doing the same trick as a steam locomotive: expand hot gas, harvest the push. When a gas expands against a piston, the work it delivers equals the pressure times the volume change: W = P × ΔV. High pressure shoving through a large volume change means big work per stroke — the entire reason turbochargers cram more air into the cylinder and why diesel engines squeeze their charge so hard.

This calculator multiplies pressure by expansion. Type the gas pressure into Variable A — in pascals for SI, or psi if you will convert after — and the volume change in cubic meters (or cubic inches, consistently) into Variable B; the Result box gives the expansion work in joules (or inch-pounds). A gearhead in Michigan analyzing a 500 cc cylinder firing at an average 150 psi, for instance, enters the converted values and reads the work each power stroke contributes. Multiply by the strokes per second and you have the engine's indicated power — before friction and heat take their cut, which is why brake horsepower always trails the thermodynamic ideal.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Thermodynamics Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.