Electrical FundamentalsFormulas - Equations

Power, Voltage, Current & Resistance Formulas For DC Circuits

Formulas for Power, Voltage, Current, and Resistance in DC Circuits

Electric Power

Electric power is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the Watt (W), equivalent to one joule per second.

Electrical power formulas in DC circuits based on Ohm’s law.

  1. P = E × I
  2. P = I2R
  3. P = E2 ÷ R


Voltage is the electric potential difference between two points. The SI unit of voltage is the Volts (V), equivalent to joules per coulomb.

Voltage formulas in DC circuits:

  1. E = I × R
  2. E = P ÷ I
  3. E = √ (P × R)

Electric Current

Electric Current is the flow of electric charge or electrons through an electrical conductor. The SI unit for measuring electric current is the Amperes (A), which represents the flow of electric charges through a surface at the rate of one coulomb per second.

Electric Current formulas in DC circuits:

  1. I = E ÷ R
  2. I = P ÷ E
  3. I = √(P ÷ R)


The electrical resistance of an electrical element is the opposition to the passage of an electric current through that element. The SI unit of electrical resistance is the Ohm (Ω).

DC Resistance formulas:

  1. R = E ÷ I
  2. R = P ÷ I2
  3. R = E2 ÷ P


  • I = Current in Amperes (A)
  • V = Voltage in Volts (V represented by E)
  • P = Power in Watts (W)
  • R = Resistance in Ohm (Ω)

Ohm’s Law Chart

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Ohm's Law Chart
Ohm’s Law Chart

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