The Ohm's Law Wheel and formulas
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance: I = V / R.
Combining Ohm's Law with Joule's Law of electric power (P = V × I) yields the complete Ohm's Law wheel, expressing each of the four fundamental electrical variables in terms of any two knowns.
Voltage formulas: V = I × R = P / I = √(P × R). Current formulas: I = V / R = P / V = √(P / R). Resistance formulas: R = V / I = V² / P = P / I². Power formulas: P = V × I = I² × R = V² / R.
Worked example: Sizing a 12V automotive circuit
An automotive auxiliary light operates on a 12V DC system and draws 2 Amperes of current.
Resistance R = V / I = 12 V ÷ 2 A = 6.0 Ohms (Ω).
Power consumption P = V × I = 12 V × 2 A = 24.0 Watts (0.024 kW).
Inputs for the Ohm's law calculator
Known values
Select the pair of electrical variables you already know (e.g. Voltage and Resistance, or Voltage and Power).
CALCULATOR QUESTIONS
Ohm's law & power wheel calculator questions
What is Ohm's Law in simple terms?
Ohm's Law describes how voltage (electric pressure), current (electric flow rate), and resistance (opposition to flow) interact in a closed circuit: Voltage = Current × Resistance (V = I × R).
How do you calculate power from voltage and resistance?
Square the voltage and divide by the resistance: P = V² / R. For example, 120V across a 100Ω resistor dissipates 120² ÷ 100 = 144 Watts.