Use this Ohm's Law Calculator to find Voltage (V), Current (I), or Resistance (R). Enter any two values, and the calculator will determine the missing one. Perfect for students, engineers, and anyone working with electrical circuits.
Ohm’s Law Explained
Ohm’s Law describes one of the most important relationships in electricity: how voltage, current, and resistance work together in a circuit. In simple terms, it tells us how much current will flow when a certain voltage is applied across a component that resists the flow of electricity.
The three key quantities
- Voltage (V) is the electrical “push” that drives charge through a circuit. It’s measured in volts (V).
- Current (I) is the rate at which electric charge flows. It’s measured in amperes (A), often called amps.
- Resistance (R) is how much a material or component opposes the flow of current. It’s measured in ohms (Ω).
What Ohm’s Law states
Ohm’s Law says that the current through a conductor is:
- directly proportional to the voltage across it (more voltage → more current), and
- inversely proportional to the resistance (more resistance → less current).
The equation
Ohm’s Law is usually written as:
- V = I × R
This can also be rearranged depending on what you need to find:
- I = V ÷ R
- R = V ÷ I
What it means in practical terms
For a two-terminal component like a resistor, if the resistance stays constant, the amount of current that flows depends entirely on the applied voltage:
- If you increase the voltage, the current increases.
- If you increase the resistance, the current decreases.
So, at a fixed voltage, a larger resistance “restricts” current more, while a smaller resistance allows more current to flow.
Examples
Example 1: Finding voltage
If a circuit or component has a resistance of 5 Ω and it needs 3 A of current:
- V = I × R = 3 A × 5 Ω = 15 V
So the required voltage is 15 volts.
Example 2: Finding power using Ohm’s Law values
Electrical power tells you how quickly energy is being used or dissipated (often as heat in a resistor). Power is calculated using:
- P = V × I
If a circuit has 20 V across it and 2 A of current flowing:
- P = 20 V × 2 A = 40 W
So the circuit dissipates 40 watts of power.
Quick summary
- Voltage drives current
- Resistance limits current
- Ohm’s Law links all three: V = I × R
