Ohms Law Calculator
Solve voltage, current, resistance and power from any two known electrical values.
Inputs
Voltage (V)
12.0000V
Current (I)
3.0000A
Resistance (R)
4.0000Ω
Power (P)
36.0000W
Step by step
Known values
= V = 12.0000 V
Ohm's Law (V = I × R)
12.0000 V = 3.0000 A × 4.0000 Ω
Power Law (P = V × I)
36.0000 W = 12.0000 V × 3.0000 A
Check: P = I² × R
36.0000 W = (3.0000 A)² × 4.0000 Ω
= 36.0000 W
How it works
Ohm's Law (V = I × R) and the Power Law (P = V × I) together define the four electrical quantities. Any two quantities uniquely determine the other two. The calculator solves all six possible input pairs: V+I, V+R, V+P, I+R, I+P, R+P. Edge cases like zero voltage, zero current or zero resistance are flagged explicitly because they indicate open or short circuits where some quantities are undefined or infinite.
Formulas
Ohm's Law
Voltage = Current × Resistance
- V
- Voltage (volts)
- I
- Current (amperes)
- R
- Resistance (ohms)
Power Law
Power = Voltage × Current = Current² × Resistance = Voltage² ÷ Resistance
- P
- Power (watts)
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law states that the voltage across a resistor is directly proportional to the current flowing through it, with the resistance as the constant of proportionality: V = I × R.
Why are there six input combinations?
There are four variables (V, I, R, P). Choosing any two gives a unique solution for the other two: C(4,2) = 6 combinations. This calculator handles all six.
What does it mean when resistance is zero?
Zero resistance is an ideal short circuit. Ohm's Law says current would be infinite (V ÷ 0), which is a real circuit fault. The calculator flags this rather than returning Infinity.
Is this valid for AC circuits?
For pure resistive loads, yes. AC circuits with capacitors or inductors have impedance (Z), not just resistance, and require phasor math. This calculator covers the resistive case.