How to Calculate Power

• 1). Using a calculator, determine the amount of energy (Joules) and time (Seconds) you wish to calculate power (Watts) by. Divide energy into time and you will get the rate of power (Watts) that is used.For example: .05(J) / 20(S)=.0025(mW)
  
  Use milliwatts because the amount of power used in most electronics is relatively low.
  
  
• 2). Determine the amount of current (Amps) and voltage (Volts) you wish to calculate power by. Multiply the number of amps and volts together. The product will give you the amount of power. For example: 001(mA) x 5(V)= .005(mW)
  
  
• 3). Look at Ohm's Law: V=IxR or voltage equals current times resistance. Using the previous formula, power equals amps times voltage (P=IxV), convert the formula to power equals current squared times resistance P=IxIxR. This will give you the calculation of power using resistance.
  
  
• 4). Squaring voltage and dividing it by resistance will also give you the amount of power. For Example:
  
  .005(mA) x .005(mA) x 50(ohms)=P
  
  .000025(mA)x 50(Ohms)=.00125(mA)