Power Calculator

These calculators perform calculations associated with power (wattage). The bottom one calculates power dissipated in a resistor given the current flowing through it.

Calculate Power from Voltage & Current (P = V * I):

Enter Voltage:        Volts Millivolts Microvolts		Power = ?
Enter Current:        Amps Milliamps Microamps

Calculate Voltage from Power & Current (V = P / I):

Enter Power:        Watts Milliwatts Microwatts		Voltage = ?
Enter Current:        Amps Milliamps Microamps

Calculate Current from Power & Voltage (I = P / V):

Enter Power:        Watts Milliwatts Microwatts		Current = ?
Enter Voltage:        Volts Millivolts Microvolts

Calculate Power Dissipated in a Resistor (P = I² * R):

Enter Current:        Amps Milliamps Microamps		Power = ?
Enter Resistance:        Ohms Kilohms Megohms

Formulae:

The formula for calculating power in DC circuits is:

P = V * I, where P is power in Watts, V is voltage in Volts and I is current in Amps

This can be re-arranged to give:

V = P / I
I = P / V

Combining this equation with Ohms Law gives the power dissipated in a resistor:

P = V * I
V = I * R (Ohms Law)
Combining these gives P = I * I * R
or P= I² * R

See here for more details.