Power Calculator

In the circuit of Figure 1, a voltage source is connected to a resistive load. As shown, a current will flow from the voltage source through the resistive load. 

Figure 1. A basic DC circuit with a voltage source and resistive load. 

Power Equation

Ohm's Law describes the relationship between the voltage, current, and resistance.  The power dissipated in the load is the voltage multiplied by the current. Therefore, to find the power, we can use any of the following power equations: 

$$P = VI = I^{2}R = \frac{V^2}{R}$$

where:

V = voltage (V)

I = current (A)

R = resistance (Ω)

P = power (W)

We can solve for any two variables given the other two. For example, given the power and current, we can solve for the resistance and voltage by rearranging the equations as follows:

$$R = \frac{P}{I^2}$$

$$V = \frac{P}{I}$$

This calculator allows you to select different units of measurement for each of the four parameters:

V = voltage in kV, V, mV, or µV

I = current in kA, A, mA, µA, nA, or pA

R = resistance in MΩ, kΩ, Ω, or mΩ 

P = power in MW, kW, W, mW, µW, nW, or pW