Ohm's Law, formulated by Georg Ohm in 1827, states that the current (I) flowing through a conductor is directly proportional to the voltage (V) and inversely proportional to the resistance (R): V = I × R. It is the foundational principle of electrical circuit analysis.

What is the difference between AC and DC in Ohm's Law?

Ohm's Law applies directly to DC (direct current) circuits. For AC (alternating current) circuits, resistance is replaced by impedance (Z), which includes both resistance and reactance from capacitors and inductors. The formula becomes V = I × Z.

What is electrical power?

Electrical power (P) is the rate at which electrical energy is transferred. It is measured in Watts (W) and calculated as P = V × I = I² × R = V²/R. A 100W light bulb consumes 100 joules of energy per second.

What is the difference between voltage and current?

Voltage (V) is the electrical potential difference - the 'pressure' that drives current through a circuit, measured in Volts. Current (I) is the flow of electric charge through the circuit, measured in Amperes. Voltage is the cause; current is the effect (for a given resistance).

Why does resistance increase with temperature?

In most conductors (metals), resistance increases with temperature because thermal vibration of atoms increases, impeding the flow of electrons. This is described by the temperature coefficient of resistance. In semiconductors, the opposite occurs - resistance decreases with temperature.

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Ohm's Law Calculator

Calculate voltage, current, resistance, and power using Ohm's Law. Essential for electronics and electrical engineering.

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V = I × R | P = V × I = I² × R = V² / R

Variables

VVoltage in Volts (V)

ICurrent in Amperes (A)

RResistance in Ohms (Ω)

PPower in Watts (W)

Explanation

Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points. The constant of proportionality is the resistance. Power is the rate of energy transfer, calculated as voltage times current.

What is the Ohm's Law Calculator?

Ohm's Law is the cornerstone of electrical engineering and electronics. Whether you are designing circuits, troubleshooting electrical systems, or studying physics, understanding the relationship between voltage, current, resistance, and power is essential. This calculator makes it easy to solve for any of these four quantities given any two known values.

How to Use This Calculator

Select the two known electrical quantities and enter their values with appropriate units. The calculator automatically determines all four quantities - voltage, current, resistance, and power - with step-by-step calculations showing the formulas used.

Worked Examples

12 V across a 2 A load

You measure 12 volts and 2 amperes in a simple DC circuit and want the resistance and power.

R = V ÷ I: 12 ÷ 2 = 6 Ω
P = V × I: 12 × 2 = 24 W

Resistance 6 Ω, power dissipated 24 W.

0.5 A through a 100 Ω resistor

Known current and resistance — solve for voltage and power.

V = I × R: 0.5 × 100 = 50 V
P = I² × R: 0.25 × 100 = 25 W

Voltage 50 V, power 25 W.

Enter current in amps, not milliamps — 500 mA and 0.5 A are the same thing.

Why Use MyCalculatorsHub's Ohm's Law Calculator?

This calculator supports multiple unit inputs (milliamps, kilohms) and automatically converts them, eliminating a common source of calculation errors. It is suitable for students learning circuit theory, hobbyists working on electronics projects, and professionals needing quick calculations.

Common Mistakes to Avoid

A common mistake is mixing up units - for example, entering current in milliamps but treating it as amperes. This calculator handles unit conversion automatically. Also, Ohm's Law assumes linear (ohmic) behavior; non-linear components like diodes and transistors do not follow Ohm's Law.