Ohm's Law Calculator
Solve Ohm's law (V = I × R) for voltage, current, or resistance, and get the power (P = V × I). Enter any two values to find the rest.
Voltage (V)
12 V
Power (P = V × I)
24 W
Ohm's law: V = I × R. Power: P = V × I. Units — volts (V), amperes (A), ohms (Ω), watts (W).
Frequently Asked Questions
What is Ohm's law?
Ohm's law states that the voltage (V) across a conductor is equal to the current (I) flowing through it multiplied by its resistance (R): V = I × R. It is the foundational relationship in electrical circuit analysis.
How do I calculate voltage from current and resistance?
Multiply the current by the resistance: V = I × R. For example, a 2 A current through a 10 Ω resistor produces 2 × 10 = 20 volts.
How do I find current from voltage and resistance?
Rearrange Ohm's law to I = V / R. Divide the voltage by the resistance. For example, 12 V across 4 Ω gives 12 / 4 = 3 amps.
How do I calculate resistance?
Rearrange to R = V / I. Divide the voltage by the current. For example, 9 V drawing 0.5 A means R = 9 / 0.5 = 18 ohms.
How is electrical power related to Ohm's law?
Power is voltage times current: P = V × I, measured in watts. Combined with Ohm's law you can also write P = I²R or P = V²/R, so power can be found from any two of voltage, current, and resistance.
What are the SI units used in Ohm's law?
Voltage is measured in volts (V), current in amperes (A), resistance in ohms (Ω), and power in watts (W). All formulas here assume these base SI units.