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Energy, electricity and mechanics

Ohm's law and power

Calculates voltage, current, resistance and power from two of them.

V

Potential difference between the two points of the circuit.

A

Current flowing through the circuit.

Result

Voltage
— V
Current
— A
Resistance
— Ω
Power
— W

How it is calculated

Ohm's law: V = I × R (voltage in volts, current in amperes, resistance in ohms). Power: P = V × I = I² × R = V² ÷ R.

With two known magnitudes, the other two are found by combining both formulas. For example, knowing power and resistance: I = √(P ÷ R) and V = √(P × R).

Keep in mind

  • From 50 V in alternating current (or 120 V in direct current) direct contact is dangerous; below that it is considered extra-low safety voltage in dry environments.
  • This calculator is for simple resistive circuits (direct current or purely resistive loads in AC). It does not replace an electrical design project or installation regulations (in Spain, the REBT).
  • Before working on any installation, cut the power, verify the absence of voltage, and use residual-current and circuit-breaker protection.

See also

More tools in “Energy, electricity and mechanics”