Ohm’s Law defines the linear relationship between voltage, current, and resistance in a conductor. It states that voltage (V) is equal to current (I) multiplied by resistance (R). In formula form: $V = I \times R$. This implies current is directly proportional to voltage and inversely proportional to resistance. It is a foundational law used in all electrical circuit calculations.
Given any two of the three quantities (V, I, R), the third can be found by rearrangement:
For example, if a circuit has a 12 V battery and a lamp of 6 Ω resistance, the current is calculated as: $I = 12\,V / 6\,\Omega = 2\,A$. Conversely, if 5 A flows through an 8 Ω resistor, the voltage across it is: $V = 5\,A \times 8\,\Omega = 40\,V$.
Ohm’s Law applies not just to simple resistors, but to any component or material obeying linear V-I behavior. It is used in sensor calibration, safety checks, and high-voltage testing. Even in AC circuits, Ohm’s Law is locally valid for instantaneous values or impedance (using $V = I \times Z$ for AC phasors).
This law is ubiquitous in electrical engineering. Designers use it for sizing resistors, setting circuit setpoints, and verifying that wire resistance won’t cause excessive voltage drop. Technicians apply it to troubleshoot circuits if measured values deviate from expected behavior.
Ohm’s Law itself is a natural law, so it isn’t governed by a specific standard. However, understanding Ohm’s Law is assumed in all standards and codes. For instance, the International System of Units (SI) defines the ohm (Ω) in terms of voltage and current, reinforcing $1\,\Omega = 1\,V/1\,A$.
Calculating $V = I \times R$ is simple enough to do by hand or with a basic calculator. Nevertheless, all circuit simulation tools internally apply Ohm’s Law at every node.
Use the cards below to perform calculations based on Ohm’s Law.