Ohm's Law Calculator

Calculate voltage, current, and resistance using Ohm's law. Enter any two values to find the third instantly.

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1. Select which two values you know - any combination of voltage, current, and resistance. 2. Enter the known values in their respective input fields, choosing the appropriate unit (e.g., volts, milliamps, kiloohms). 3. The calculator instantly computes the missing value along with power in watts. 4. Review all four results - voltage, current, resistance, and power - displayed below the inputs. 5. Copy any result value to use in your circuit design or homework.

About This Tool

Ohm's law is one of the most fundamental principles in electrical engineering and electronics. It describes the relationship between voltage (V), current (I), and resistance (R) in a circuit. By knowing any two of these values, you can calculate the third - making this calculator an essential tool for students, hobbyists, and professionals alike.

Whether you are designing a simple LED circuit, troubleshooting an electrical system, or studying for an exam, this calculator handles all three forms of the equation. It also computes power (P) in watts, giving you a complete picture of the electrical characteristics at any point in a circuit.

This tool supports a wide range of input units including milliamps, kiloohms, and millivolts, so you can work with values at any scale without manual conversion.

Formula / How It Works

V = I x R | I = V / R | R = V / I | P = V x I | P = I^2 x R | P = V^2 / R

Frequently Asked Questions

Ohm's law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance. It is expressed as V = I x R, where V is voltage in volts, I is current in amps, and R is resistance in ohms.
Power can be derived from Ohm's law using the formulas P = V x I, P = I squared x R, or P = V squared / R. This calculator automatically computes power when you provide any two of the three primary values (voltage, current, resistance).
Ohm's law applies to ohmic materials - those where resistance remains constant regardless of voltage and current. Most metals and many resistors are ohmic. Non-ohmic components like diodes, transistors, and thermistors have resistance that varies with voltage or temperature.
The standard units are volts (V) for voltage, amps (A) for current, and ohms (the Greek letter omega) for resistance. Power is measured in watts (W). You can also work with milliamps (mA), kiloohms (k-ohm), megaohms (M-ohm), and millivolts (mV).
Ohm's law applies to AC circuits, but you must use impedance (Z) instead of simple resistance (R). Impedance accounts for resistance, capacitance, and inductance. For purely resistive AC loads, Ohm's law works the same as in DC circuits.

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