Ohm's Law Calculator
Lock any 2 of voltage, current, resistance, or power — the other 2 are computed automatically.
Free & unlimitedWorks offline
Lock the values you know (2 of 4 locked)
Voltage (V)
Current (A)
Resistance (Ω)
Power (W)
Formulas used
R = V / IP = V × I
Formula reference
Voltage
V = I × R
V = P / I
V = √(P × R)
Current
I = V / R
I = P / V
I = √(P / R)
Resistance
R = V / I
R = V² / P
R = P / I²
Power
P = V × I
P = V² / R
P = I² × R
All processing happens in your browser. No data is sent to any server.
About this tool
- 1
Enter two known values
Input any two of voltage (V), current (I), resistance (R), or power (P).
- 2
Calculate unknowns
The tool instantly computes the remaining two values using Ohm's law and the power equation.
- 3
Review the formulas
See which formulas were used, with the calculation steps shown for learning purposes.
- Double-check your units - the tool expects volts, amps, ohms, and watts. Convert milliamps to amps first (divide by 1000).
- For AC circuits, these calculations apply to RMS values only. Complex impedance requires different formulas.
- Use this alongside the LED resistor calculator when designing simple LED circuits.
- Calculates voltage, current, resistance, and power from any two inputs
- Shows all applicable Ohm's law and power formulas used
- Unit-aware input: enter values in mA, kΩ, mW, etc.
- Visual Ohm's law wheel/triangle diagram
- Step-by-step calculation breakdown
- Determining the current draw of a component given voltage and resistance
- Calculating power dissipation to choose the right resistor wattage rating
- Finding the voltage drop across a resistor in a circuit
- Quick sanity checks during electronics prototyping and debugging