Ohm's Law Calculator

Calculate voltage, current, resistance, and electrical power using Ohm's Law (V = IR) and power formulas.

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About Ohm's Law

Ohm's Law

Ohm's Law is one of the most fundamental principles in electrical engineering and physics. It states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them. The law is expressed as: V = I × R

The Three Forms

• V = I × R - Voltage equals current times resistance
• I = V / R - Current equals voltage divided by resistance
• R = V / I - Resistance equals voltage divided by current

Electrical Power

Electrical power is the rate at which electrical energy is transferred by an electric circuit. The power consumed by a circuit element can be calculated using:

• P = V × I - Power equals voltage times current
• P = I² × R - Power equals current squared times resistance
• P = V² / R - Power equals voltage squared divided by resistance

Units

• Voltage (V): V (Volts), mV (millivolts), kV (kilovolts)
• Current (I): A (Amperes), mA (milliamperes), μA (microamperes)
• Resistance (R): Ω (Ohms), kΩ (kilohms), MΩ (megohms)
• Power (P): W (Watts), mW (milliwatts), kW (kilowatts)

Examples

• A circuit with 12V and 4Ω has current I = 12/4 = 3 A
• If 2A flows through 6Ω, voltage V = 2 × 6 = 12 V
• A 9V battery powering 0.5A draws power P = 9 × 0.5 = 4.5 W
• A 100Ω resistor with 5V across it dissipates P = 5²/100 = 0.25 W

Applications

• Designing electronic circuits and selecting components
• Calculating current draw and power consumption
• Determining appropriate wire gauge for electrical wiring
• Troubleshooting electrical systems
• Battery life estimation

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