Calculators

Voltage, Current & Resistance Calculator

Use Ohm's law to calculate voltage, current or resistance. Enter any two known values and the calculator will determine the third value.

Ohm's Law

Ohm's law describes the relationship between voltage, current and resistance in an electrical circuit.

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The three basic relationships are:

Voltage is the electrical potential difference between two points. It is measured in volts (V).

If current and resistance are known, voltage can be calculated from their product.

Electric current describes the flow of electric charge through a circuit. It is measured in amperes (A).

If voltage and resistance are known, current can be calculated.

Resistance opposes the flow of electric current. It is measured in ohms (Ω).

If voltage and current are known, resistance can be calculated.

Suppose a 12 V supply is connected to a 6 Ω resistor.

Voltage = 12 V
Resistance = 6 Ω

Current = 12 ÷ 6

Current = 2 A

The circuit current is therefore 2 A.

Suppose a circuit has a current of 2 A flowing through a 10 Ω resistor.

Current = 2 A
Resistance = 10 Ω

Voltage = 2 × 10

Voltage = 20 V

The voltage across the resistor is therefore 20 V.

Suppose a circuit has 24 V across a load and the current is 3 A.

Voltage = 24 V
Current = 3 A

Resistance = 24 ÷ 3

Resistance = 8 Ω

The resistance is therefore 8 Ω.

Voltage (V)

Current (A)

Resistance (Ω)

Enter any two values and click Calculate.

Voltage and current can also be used to calculate electrical power.

Power is measured in watts (W).

Power = Voltage × Current

For example, a 12 V circuit drawing 2 A consumes:

Power = 12 × 2
Power = 24 W

Voltage is measured in volts (V).
Current is measured in amperes (A).
Resistance is measured in ohms (Ω).
Use consistent units when performing calculations.
Ohm's law applies directly to resistive relationships; real components can have more complex behavior.
Do not confuse electrical resistance with impedance in AC circuits.