Solve the most-used physics formulas
Many school and college physics problems come down to a handful of core formulas from mechanics and electricity. This calculator lets you pick a formula and solve for whichever quantity is unknown, so you can check homework, prepare for exams or do quick engineering estimates. All values use SI units, the international standard used in science.
How to use the calculator
- Choose a formula.
- Choose which quantity you want to find. The input boxes change to show the values you need.
- Enter the known values in SI units, such as kilograms, metres and seconds. The answer and the formula appear immediately.
The formulas
| Formula | Meaning | Example |
|---|---|---|
| F = m × a | Newton's second law: force equals mass times acceleration | A 1,200 kg car accelerating at 2.5 m/s² needs 3,000 N |
| W = F × d | Work done by a force moving an object a distance in its direction | Pushing with 50 N for 12 m does 600 J of work |
| P = W ÷ t | Power is the rate of doing work | 3,000 J in 60 s is 50 W |
| KE = ½mv² | Energy of a moving object | A 70 kg runner at 8 m/s has 2,240 J |
| PE = mgh | Gravitational potential energy near Earth's surface | 2 kg lifted 10 m gains 196.2 J |
| p = m × v | Momentum | A 160 g cricket ball at 40 m/s has 6.4 kg·m/s |
| ρ = m ÷ V | Density | 7.9 kg of steel in 0.001 m³ is 7,900 kg/m³ |
| V = I × R | Ohm's law for electric circuits | 0.5 A through 440 Ω needs 220 V |
Tips for correct answers
- Convert units first: grams to kilograms (÷ 1,000), km/h to m/s (÷ 3.6), minutes to seconds (× 60). Mixing units is the most common mistake. The Unit Converter can help.
- Gravity: g = 9.81 m/s² on Earth. Some textbooks use 9.8 or 10; change it in the potential energy formula if needed. On the Moon, g ≈ 1.62 m/s².
- Doubling speed quadruples kinetic energy, because v is squared. That is why speed has such a big effect on road accidents.
Frequently asked questions
What is a joule?
The SI unit of energy and work: 1 J is the work done by a force of 1 newton over 1 metre.
How do I calculate speed, distance or time?
Use the dedicated Speed, Distance and Time Calculator.
Does it handle electrical power?
For electrical power, use P = V × I. Find V or I with Ohm's law here, then multiply.