About this Ohms Law
Ohm's Law is the most fundamental equation in electronics, describing the relationship between Voltage, Current, and Resistance. This tool combines Ohm's Law with the Power Law to solve for any parameter in a DC circuit.
Who this calculator is for
- Electronics students, makers, and technicians solving basic DC circuit values.
- Anyone checking a resistor, power supply, LED, or load calculation quickly.
- Engineers validating whether a known pair of electrical values is internally consistent.
When to use it
- Use it when you know any two circuit values and want the other two.
- Use it to estimate current draw, resistance, or power for a DC load.
- Use it before choosing a resistor, fuse, wire size, or power supply rating.
How to use this calculator
- You must enter exactly two values.
- Leave the other fields as 0.
- The tool computes the two missing variables.
Key assumptions
- The calculator expects exactly two known positive inputs and treats 0 as unknown.
- This tool models a simple resistive circuit using DC-style Ohm's Law and Power Law relationships.
- Invalid combinations, such as fewer or more than two known values or division by zero, return an invalid state.
Accuracy and testing
Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.
How this calculator works
The calculator uses variations of two primary formulas:
1. Ohm's Law: $V = I \times R$ (Voltage = Current × Resistance)
2. Power Law: $P = V \times I$ (Power = Voltage × Current)
Inputs explained
Voltage (V)
Electrical potential difference, measured in Volts. The 'pressure' pushing electrons.
Current (I)
The rate of electron flow, measured in Amps.
Resistance (R)
Opposition to current flow, measured in Ohms (Ω).
Power (P)
The rate of energy usage, measured in Watts.
Understanding your results
The result completes the circuit parameters. For example, if you know a heater uses 1500 Watts at 120 Volts, the calculator finds it draws 12.5 Amps and has 9.6 Ohms resistance.
Example scenarios
Find Current
12V Battery, 4 Ohm Resistor. I = V/R = 12/4 = 3 Amps.
Find Power
120V Supply, 0.5 Amps. P = V*I = 120 * 0.5 = 60 Watts.
Key Features
- Solves for V, I, R, P
- Validates input combinations
- Physics-based logic
Tips & Best Practices
- Entering 0 is treated as 'unknown'.
- Be careful with units. 1 kΩ = 1000 Ω. 1 mA = 0.001 A. This tool expects base units (Volts, Amps, Ohms, Watts).
Glossary of Terms
- Ohm (Ω)
- Unit of resistance.
- Ampere (A)
- Unit of electric current.
- Watt (W)
- Unit of power.