Ohm's Law Calculator — Voltage, Current, Resistance & Power
Calculate voltage, current, resistance, and power using Ohm's Law. Enter any two values to find all four electrical quantities with formulas.
Enter any two values to calculate the others automatically.
Examples:
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Voltage (V)
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Current (A)
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Resistance (Ω)
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Power (W)
Formulas Used
Ohm's Law Formulas
Voltage
V = IR
V = P/I
V = √(PR)
Current
I = V/R
I = P/V
I = √(P/R)
Resistance
R = V/I
R = V²/P
R = P/I²
Power
P = VI
P = I²R
P = V²/R
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law states that voltage (V) equals current (I) times resistance (R): V = IR. It describes the relationship between these three fundamental electrical quantities in a resistive circuit.
What are the units of V, I, R, and P?
Voltage (V): Volts (V). Current (I): Amperes (A). Resistance (R): Ohms (Ω). Power (P): Watts (W). Common prefixes: mA = milliampere = 0.001 A; kΩ = kiloohm = 1000 Ω; mW = milliwatt = 0.001 W.
How is electrical power calculated?
Power = Voltage × Current: P = VI. Combined with Ohm's Law, P = I²R = V²/R. Power measures how fast energy is used or generated, measured in Watts.
What is the Ohm's Law triangle?
The triangle has V at top, I and R at bottom. Cover the unknown: V = I×R, I = V/R, R = V/I. Power forms a similar relationship: P = VI, I = P/V, V = P/I.
When does Ohm's Law not apply?
Ohm's Law applies to linear (ohmic) resistors at constant temperature. It does not apply to non-linear devices like diodes, LEDs, transistors, or when temperature changes significantly alter resistance.