Ohm's Law states that voltage (V) equals current (I) multiplied by resistance (R): V = I × R. It describes the relationship between voltage, current, and resistance in a resistive circuit. From this, I = V/R and R = V/I.

Voltage is measured in Volts (V), current in Amperes (A), resistance in Ohms (Ω), and power in Watts (W). Enter values in base units. The calculator outputs results with SI prefixes: milliamps (mA), kilohms (kΩ), milliwatts (mW), etc.

V = I × R P = V × I Any 2 of 4 values

Ohm's Law Calculator

Enter any two values — voltage (V), current (I), resistance (R), or power (P) — to calculate the remaining two. Results displayed with SI prefixes.

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Voltage (V)	—
Current (I)	—
Resistance (R)	—
Power (P)	—

Formula Reference

Find	Formula
Voltage V	I × R \| P / I \| √(P×R)
Current I	V / R \| P / V \| √(P/R)
Resistance R	V / I \| V²/P \| P/I²
Power P	V × I \| I²×R \| V²/R

Ohm's Law Explained

V = I × R

Ohm's Law relates voltage (V in volts), current (I in amperes), and resistance (R in ohms). For a given resistance, doubling the voltage doubles the current. For a given voltage, doubling the resistance halves the current. This linear relationship holds for resistors at constant temperature.

P = V × I

Electrical power (P in watts) is the rate at which energy is transferred. P = V × I, which combined with Ohm's Law gives P = I² × R (useful when resistance and current are known) and P = V² / R (useful when voltage and resistance are known). Power is always positive for resistive elements.

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FAQ

What is Ohm's Law?

Ohm's Law states that voltage V equals current I times resistance R: V = I × R. Rearranged: I = V/R and R = V/I. It describes the linear relationship between voltage, current, and resistance in a resistive circuit at constant temperature.

What is the power formula?

Electrical power P = V × I (watts). Combined with Ohm's Law: P = I² × R and P = V² / R. These four formulas allow you to calculate any unknown when any two of V, I, R, or P are known.

What units are used?

Voltage in Volts (V), current in Amperes (A), resistance in Ohms (Ω), power in Watts (W). Enter values in base units. Results are shown with SI prefixes: mA (milliamps = 0.001 A), kΩ (kilohms = 1,000 Ω), mW (milliwatts = 0.001 W).

Does Ohm's Law apply to all components?

Ohm's Law applies exactly to ideal resistors. Real-world resistors follow it closely at constant temperature. However, non-linear components like diodes, transistors, capacitors, and inductors do not follow Ohm's Law — their V-I relationship is non-linear or frequency-dependent.