Ohm's Law Calculator

Ohm's Law is one of the most fundamental principles in electrical engineering, stating that the current flowing through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. Expressed as V = I × R (voltage equals current times resistance), this simple equation governs the behavior of every electrical circuit from household wiring to complex electronic devices. Engineers use Ohm's Law to design circuits, select appropriate components, and troubleshoot problems. Electricians apply it when sizing wire gauges and selecting fuses. Students encounter it as one of the first concepts in physics and electronics courses. This calculator lets you enter any two of the three values — voltage (V), current (I in amps), and resistance (R in ohms) — and instantly computes the third. It also calculates power (P = V × I) for the given parameters. All computations run entirely in your browser using JavaScript arithmetic, making this a fast, private, and always-available reference tool for anyone working with electrical systems.

The calculator implements the four fundamental forms of Ohm's Law: V = I × R, I = V / R, R = V / I, and the power equation P = V × I (which can also be expressed as P = I²R or P = V²/R). When you enter two known values, the tool determines which formula to apply and solves for the unknowns. It uses standard IEEE double-precision floating-point arithmetic in JavaScript, providing accuracy sufficient for all practical electrical calculations. Input validation ensures that resistance cannot be zero (which would imply infinite current) and that negative values are flagged appropriately. The results display includes derived values: if you enter voltage and resistance, you get current and power; if you enter current and resistance, you get voltage and power. The calculator also shows the relationship visually, helping students understand how changing one variable affects the others. Everything is computed locally in your browser — no electrical data, measurements, or project details are sent to any server.