Ohm's Law Calculator

Ohm's Law, discovered by Georg Simon Ohm in 1827, defines the fundamental relationship between voltage (V), current (I), and resistance (R) in electrical circuits: V = I × R. This principle forms the foundation for all circuit analysis, design, and troubleshooting in electrical engineering.

Core Relationships: The law states that current through a conductor is directly proportional to voltage and inversely proportional to resistance. With any two values known, the third can be calculated—making circuit behavior predictable and enabling precise component sizing, safety analysis, and power calculations.

Practical Applications: Engineers use Ohm's Law daily for sizing conductors (calculating voltage drop and current capacity), selecting resistors and fuses, troubleshooting circuits by comparing calculated vs. measured values, and determining power dissipation (P = I²R) for thermal management. A 120V circuit with 10Ω resistance draws 12A current and dissipates 1,440W of power.

Important Limitations: Ohm's Law applies only to linear, resistive elements at constant temperature. Non-ohmic devices (diodes, transistors, LEDs) have variable resistance. Temperature changes alter resistance—copper increases ~0.4% per $°$C. AC circuits require impedance (Z) instead of pure resistance, accounting for capacitive and inductive reactance.

Circuit Configurations: In series circuits, current is constant and resistances add (Rtotal = R1 + R2 + ...). In parallel circuits, voltage is constant and reciprocal resistances add (1/Rtotal = 1/R1 + 1/R2 + ...). Complex circuits combine both configurations, requiring systematic application of Ohm's Law with Kirchhoff's laws.

Standards Reference: IEC 60038 defines standard voltages. IEEE 141 applies Ohm's Law principles to industrial power systems. NEC Article 310 uses Ohm's Law for conductor ampacity calculations.