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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):

Power = ?

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

Voltage = ?

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

Current = ?

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

Power = ?


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.

If you found this calulator useful you should try Electronics Assistant!

Electronics Assistant
  • All the online calculators and more in a stand-alone application
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  • Calculation of nearest preferred resistor values with a choice of 5 series from E12 to E192
  • Print & save calculation results