SolveMyPhysics
Free physics calculators that solve in every direction and show the rearranged formula. Acceleration, velocity, force, energy, momentum, torque, density and pressure.
Solve in any direction
Every calculator rearranges for whichever variable you are missing, not just the one in the page title.
Real units
m/s, km/h, mph, ft/s, newtons, pound-force, psi, bar — converted with the exact factors NIST publishes.
The formula it used
Each answer shows the rearranged equation and your own numbers substituted into it.
Motion & Kinematics
Energy, Work & Power
Why solve in every direction?
Most physics formulas are a single equation relating three or four quantities, which means knowing all but one of them determines the last. a = (v − u) ÷ t is also v = u + a·t, and u = v − a·t, and t = (v − u) ÷ a — the same physical relationship, rearranged. Yet most calculators only ever solve the direction in their page title, so the moment your homework asks for the time rather than the acceleration, the tool stops being useful.
Every calculator here exposes all of those directions, and tells you which rearrangement it applied. It also refuses the questions that genuinely have no answer rather than returning a misleading number: solving for time at zero acceleration, or for force from work done at exactly ninety degrees, produces an explanation instead of a figure, because in both cases no value of the missing variable can satisfy the physics.
Units are part of the problem
Real problems rarely arrive in tidy SI units. A car's speed is in mph, a spanner is measured in millimetres, a tyre pressure is in psi, and a physics textbook wants all of it in metres, kilograms and seconds. Converting by hand before you start is where a surprising share of wrong answers come from.
Each input here carries its own unit selector, and the result can be displayed in any unit of the right kind. The conversion happens inside the calculation, so the physics only ever sees SI values and you never have to do the arithmetic twice.
Where the numbers come from
Standard gravity is taken as exactly 9.80665 m/s² and standard atmosphere as exactly 101,325 Pa, both defined constants published by NIST rather than measured approximations. Unit conversions use the factors in the NIST Guide to the SI: a foot is exactly 0.3048 m, a mile per hour is exactly 0.44704 m/s, and an avoirdupois pound is exactly 0.45359237 kg.
Surface gravity figures for other planets come from NASA's Planetary Fact Sheet. Newtonian mechanics itself does not change, which is the quiet advantage of this subject: a correct answer here stays correct indefinitely.