Ohm's Law Calculator
Find voltage, current, or resistance instantly using Ohm's Law. Essential for electronics hobbyists, electricians, and students designing or troubleshooting circuits.
About this calculator
Ohm's Law is the foundational relationship between voltage, current, and resistance in an electrical circuit. The core formula is V = I × R, where V is voltage in volts (V), I is current in amperes (A), and R is resistance in ohms (Ω). Rearranged, you get I = V / R and R = V / I, allowing you to solve for any one variable when the other two are known. This law applies to linear, resistive components and is the starting point for almost all circuit analysis. It was formulated by Georg Simon Ohm in 1827 and remains indispensable in both AC and DC circuit design. Understanding this relationship helps you select correct resistors, fuses, and wire gauges for safe and efficient circuits.
How to use
Suppose you have a 12 V battery connected to a resistor and you measure 2 A of current flowing through the circuit. To find the resistance, use R = V / I. Plug in the values: R = 12 V / 2 A = 6 Ω. Alternatively, if you know the resistance is 6 Ω and the voltage is 12 V, you can confirm the current: I = 12 / 6 = 2 A. Enter any two known values into the calculator and it instantly solves for the third.
Frequently asked questions
What is Ohm's Law and why is it important in electronics?
Ohm's Law states that the voltage across a conductor equals the current through it multiplied by its resistance: V = I × R. It is important because it lets engineers and hobbyists predict how a circuit will behave before building it. By knowing any two of the three quantities, you can always calculate the third. It underpins resistor selection, power supply design, and fault diagnosis in almost every electrical system.
How do I calculate resistance using Ohm's Law?
To calculate resistance, rearrange the formula to R = V / I. Measure or note the voltage across the component in volts and the current through it in amperes. Dividing voltage by current gives you resistance in ohms (Ω). For example, 9 V across a component carrying 0.5 A gives R = 9 / 0.5 = 18 Ω. This is particularly useful when selecting current-limiting resistors for LEDs or other sensitive components.
When does Ohm's Law not apply?
Ohm's Law applies only to ohmic (linear) conductors, meaning components whose resistance stays constant regardless of voltage or current. It does not accurately describe non-linear components such as diodes, transistors, LEDs, or electrolytic capacitors. In those cases, the current-voltage relationship is governed by more complex models. Temperature also affects resistance in metals and semiconductors, so Ohm's Law is an approximation at extreme temperatures even for resistors.