⚡ Ohm's Law Calculator

Ohm's Law is the most fundamental relationship between Voltage (V), Current (I), and Resistance (R) in an electrical circuit.

V = I × R

In other words, voltage equals current multiplied by resistance. Rearranging the formula also gives current (I = V ÷ R) and resistance (R = V ÷ I). First published by German physicist Georg Ohm in 1827, it remains the starting point for electronics and circuit design today.

Power (P) is the energy consumed per unit time, and can be calculated three ways:

P = V × I (voltage × current)
P = I² × R (current squared × resistance)
P = V² ÷ R (voltage squared ÷ resistance)

Combined with Ohm's Law (V=IR), knowing any 2 of V, I, R, P lets you derive the other 2. This calculator automatically picks the right formula based on which pair of values you enter (V-I, V-R, V-P, I-R, I-P, R-P).

For example, connecting a 6Ω resistor to a 12V battery gives current I = V ÷ R = 12 ÷ 6 = 2A, and power consumption P = V × I = 12 × 2 = 24W.

Ohm's Law is used throughout practical work: selecting resistor values, sizing fuses, and wiring design. However, calculating voltage drop over a wire's length and gauge requires knowing the conductor's resistivity in addition to Ohm's Law — that is out of scope for this calculator and is covered by a separate voltage-drop calculator.