Engineering

Ohm's Law Calculator — Free 2026

Enter any two electrical values to instantly calculate the other two using Ohm's Law and the power equation.

Enter any 2 values and leave the others blank. The calculator will solve for the unknowns.

Voltage (V) Please enter a valid number.

Current (A) Please enter a valid number.

Resistance (Ohms) Please enter a valid number.

Power (W) Please enter a valid number.

Results

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Voltage (V)

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Current (A)

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Resistance (Ohms)

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Power (W)

How It Works

Enter any two known values
View calculated results
Clear and recalculate

Understanding Ohm's Law

Ohm's Law is one of the most fundamental principles in electrical engineering and electronics. Discovered by German physicist Georg Simon Ohm in 1827, it describes the relationship between voltage, current, and resistance in an electrical circuit. The law states that the current flowing through a conductor is directly proportional to the voltage applied across it and inversely proportional to its resistance. This simple relationship, expressed as V = I × R, forms the foundation for nearly all circuit analysis and design.

The Ohm's Law Wheel

When combined with the power equation (P = V × I), Ohm's Law yields a set of twelve useful formulas commonly arranged in a circular diagram called the Ohm's Law Wheel. From just two known values, you can derive the other two. For example, knowing voltage and resistance lets you find current (I = V / R) and power (P = V² / R). This calculator implements all twelve combinations, so you never need to remember which formula to use — just enter what you know and get instant answers.

Practical Applications

Ohm's Law is used daily by electricians, engineers, hobbyists, and students. Common applications include sizing resistors for LED circuits (see our LED resistor calculator), designing voltage dividers for sensor circuits (try the voltage divider calculator), calculating wire gauge requirements, troubleshooting circuits with a multimeter, and determining power consumption of electrical devices. Whether you are building a simple battery-powered project or designing a complex power supply, Ohm's Law is your starting point.

Limitations of Ohm's Law

While Ohm's Law is incredibly useful, it has limitations. It applies strictly to ohmic materials — conductors whose resistance remains constant regardless of voltage and current. Many real-world components are non-ohmic: diodes conduct in only one direction, transistors have variable resistance controlled by a gate signal, and thermistors change resistance with temperature. For AC circuits, impedance replaces simple resistance, incorporating capacitive and inductive reactance. Despite these caveats, Ohm's Law remains the essential starting point for understanding and designing electrical circuits.

Frequently Asked Questions

What is Ohm's Law?

Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance. The formula is V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms.

How do I calculate power using Ohm's Law?

Power can be calculated using several formulas derived from Ohm's Law: P = V × I (voltage times current), P = I² × R (current squared times resistance), or P = V² / R (voltage squared divided by resistance). All three formulas give the same result in watts.

Why do I only need to enter two values?

Ohm's Law and the power equation together form a system where any two known electrical quantities can determine the other two. For example, if you know voltage and current, you can calculate resistance (R = V/I) and power (P = V × I) directly.

Does Ohm's Law apply to all circuits?

Ohm's Law applies to ohmic (linear) conductors where resistance remains constant regardless of voltage. Non-ohmic devices like diodes, transistors, and thermistors have resistance that changes with voltage or temperature, so Ohm's Law is only an approximation for those components.