What is Ohm's Law?
Ohm's Law states that the current passing through a conductor between two points is directly proportional to the voltage across the two points. It is one of the most fundamental principles in electrical engineering and physics.
Where:
- V = Voltage in Volts (V)
- I = Current in Amperes (A)
- R = Resistance in Ohms (Ω)
Ohm's Law Power Formulas
Power (P) is the rate at which electrical energy is transferred by an electric circuit. Combining Ohm's Law with Watt's Law allows us to solve for Power alongside Voltage, Current, and Resistance.
From these two fundamental equations, we can derive the famous "Ohm's Law Pie Chart" or "Ohm's Law Wheel", which provides 12 different formulas.
| To Find | Given V & I | Given V & R | Given I & R | Given P & V | Given P & I | Given P & R |
|---|---|---|---|---|---|---|
| Voltage (V) | - | - | V = I × R | V = P / I | - | V = √(P × R) |
| Current (I) | - | I = V / R | - | I = P / V | - | I = √(P / R) |
| Resistance (R) | R = V / I | - | - | R = V² / P | R = P / I² | - |
| Power (P) | P = V × I | P = V² / R | P = I² × R | - | - | - |
Frequently Asked Questions
Simply enter any TWO known values (for example, Voltage and Resistance) into the calculator above, and click 'Calculate'. It will immediately compute the remaining two missing values (Current and Power).
Ohm's Law states that the voltage (V) across a conductor is directly proportional to the current (I) flowing through it, with resistance (R) as the constant of proportionality: V = I × R. It was formulated by German physicist Georg Simon Ohm in 1827.
The four core formulas derived from Ohm's Law are: V = I × R (Voltage = Current × Resistance); I = V / R (Current = Voltage ÷ Resistance); R = V / I (Resistance = Voltage ÷ Current); P = V × I (Power = Voltage × Current). Together these form the Ohm's Law Wheel.
Voltage is measured in Volts (V), Current is measured in Amperes (A), Resistance is measured in Ohms (Ω), and Power is measured in Watts (W).
If a 12V car battery is connected to a 6Ω resistor, the current flowing through the circuit is I = V / R = 12 / 6 = 2 Amperes. The power dissipated is P = V × I = 12 × 2 = 24 Watts.
Ohm's Law applies to ohmic conductors — materials where resistance stays constant regardless of voltage or current, such as most metals at constant temperature. It does NOT apply to non-ohmic devices like diodes, transistors, LEDs, and thermistors, where resistance changes with operating conditions.