Ohm's Law Calculator

Comprehensive Guide to Ohm's Law

If you want to understand how electricity works, you must master Ohm's Law. It is the absolute foundational equation of electrical engineering, describing the unbreakable physical relationship between Voltage, Current, and Resistance in any circuit.

Whether you are an electrician sizing a breaker box, an engineering student doing homework, or a hobbyist trying to wire LEDs without burning them out, the Ohm's Law Calculator instantly solves the algebraic triangle, providing the exact electrical values you need to build safe, functional circuits.

How to Use the Ohm's Law Calculator

Ohm's Law dictates that if you know any TWO variables in a circuit, you can instantly calculate the third.

1. Select What to Solve For: Choose whether you want to find Voltage (V), Current (I), Resistance (R), or Power (P).
2. Enter the Knowns: Input the two values you already know.
3. Calculate: The tool will instantly apply the appropriate algebraic rearrangement to output your missing value.

The Formula

The core of Ohm's Law is a single, beautiful equation developed by Georg Ohm in 1827:

V = I * R

Where:
V = Voltage (measured in Volts)
I = Current (measured in Amps)
R = Resistance (measured in Ohms)

The Ohm's Law Triangle

The equation can be algebraically rearranged into three forms depending on what you need to solve:

• To find Voltage: V = I * R
• To find Current: I = V / R
• To find Resistance: R = V / I

Watt's Law (Power)

Ohm's Law is often combined with Watt's Law to determine the total Power consumption of the circuit.

• To find Power: P = V * I (measured in Watts)

Practical Examples

Scenario 1: Wiring an LED You are building an electronics project using a 9 Volt battery. You want to power an LED that requires exactly 0.02 Amps (20mA) of current. To prevent the LED from exploding, you must add a resistor. What size resistor do you need?

• Formula: R = V / I
• R = 9V / 0.02A
• R = 450 Ohms Result: You must wire a 450-ohm resistor into the circuit to safely limit the current.

Scenario 2: Sizing a Circuit Breaker You buy a powerful space heater that consumes 1500 Watts of power. You plug it into a standard US 120 Volt wall outlet. Will it trip your standard 10-Amp circuit breaker?

• Formula: I = P / V
• I = 1500W / 120V
• I = 12.5 Amps Result: Yes! The heater pulls 12.5 Amps, which will immediately trip a standard 10-Amp breaker. You must plug it into a 15-Amp or 20-Amp circuit.

Conclusion

You cannot "guess and check" when working with electricity. Ohm's Law is the strict mathematical rulebook that governs every electron flowing through your wires. By using the Ohm's Law Calculator, you ensure your circuits are perfectly balanced, your components are protected, and your electrical designs are fundamentally safe.