Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit. It 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 between them.

What are the units used in Ohm's Law?

Voltage is measured in Volts (V), current in Amperes (A), resistance in Ohms (Ω), and electrical power in Watts (W).

Why is Ohm's Law important?

Ohm's Law helps engineers and technicians design electrical circuits, analyze electrical behavior, and ensure that electrical components operate safely within their limits.

Can Ohm's Law be used in AC circuits?

Yes, but in AC circuits impedance replaces resistance and additional factors like phase angle must be considered.

Ohm's Law Calculator

Professional Ohm's Law calculator to solve for voltage, current, resistance, and power. Easy to use with unit prefix support and formulas.

Get instant, accurate results

What is this?

Ohm's Law is a fundamental principle in electrical engineering that describes the mathematical relationship between voltage, current, and resistance in an electrical circuit.

How to Use the Ohm's Law Calculator

Ohm’s Law is one of the most important principles in electrical engineering and electronics. It explains the mathematical relationship between voltage (V), current (I), and resistance (R) in an electrical circuit. Understanding how these values interact allows engineers, electricians, students, and hobbyists to design circuits safely and efficiently.

Ohm's Law states that the voltage across a conductor is directly proportional to the current flowing through it and inversely proportional to its resistance. This simple yet powerful formula helps determine how electricity behaves in wires, components, and entire electrical systems.

The Ohm’s Law Calculator simplifies electrical calculations by allowing you to input known values and instantly calculate the unknown ones. Instead of manually rearranging formulas or performing calculations by hand, the calculator automatically determines voltage, current, resistance, and power using the correct formulas.

This tool is useful for many real-world applications including circuit design, electrical troubleshooting, educational learning, and DIY electronics projects. Whether you are working with batteries, power supplies, resistors, or microcontroller circuits, Ohm’s Law helps ensure safe and efficient electrical performance.

1. Enter Two Known Electrical Values

The calculator requires at least two known values to determine the remaining electrical parameters.

You may enter any two of the following electrical quantities:

• Voltage (V) – electrical potential difference
• Current (I) – the flow of electric charge
• Resistance (R) – opposition to current flow
• Power (P) – electrical energy consumed per second

Once two values are entered, the calculator automatically calculates the remaining values using Ohm’s Law and related power equations.

2. Select the Correct Measurement Units

Electrical measurements can be expressed in different units depending on the scale of the circuit.

Common unit options include:

Voltage:

• Volts (V)
• Millivolts (mV)

Current:

• Amperes (A)
• Milliamperes (mA)

Resistance:

• Ohms (Ω)
• Kilo-ohms (kΩ)

Power:

• Watts (W)
• Milliwatts (mW)

Selecting the correct units ensures that the calculator performs accurate conversions and calculations.

3. Run the Calculation

After entering the required values, the calculator automatically computes the unknown electrical quantities.

The results may include:

• Voltage in volts
• Current in amperes
• Resistance in ohms
• Power in watts

This helps you quickly analyze electrical circuits without performing manual calculations.

4. Review the Calculation Breakdown

The calculator also displays the formulas used to compute the results.

This helps users understand the mathematical relationship between voltage, current, resistance, and power.

Students and learners can use this information to study how electrical formulas work in real-world circuits.

Key Formulas Used in the Calculator

Ohm's Law Formula

V = I × R

This formula states that voltage is equal to current multiplied by resistance. Example: If current = 2 A Resistance = 10 Ω Voltage = 2 × 10 = 20 V

Current Calculation

I = V / R

Current can be calculated by dividing voltage by resistance. Example: Voltage = 12 V Resistance = 6 Ω Current = 12 ÷ 6 = 2 A

Resistance Calculation

R = V / I

Resistance can be calculated when voltage and current are known. Example: Voltage = 9 V Current = 3 A Resistance = 9 ÷ 3 = 3 Ω

Electrical Power Formula

P = V × I

Electrical power represents the rate at which energy is used by a circuit. Example: Voltage = 12 V Current = 2 A Power = 12 × 2 = 24 W

Power Using Current and Resistance

P = I² × R

When current and resistance are known, power can be calculated using this formula. Example: Current = 3 A Resistance = 5 Ω Power = 3² × 5 = 45 W

Power Using Voltage and Resistance

P = V² / R

If voltage and resistance are known, electrical power can be calculated using this formula. Example: Voltage = 12 V Resistance = 6 Ω Power = 144 ÷ 6 = 24 W

Benefits

Instantly calculate voltage, current, resistance, or power
Simplifies electrical circuit calculations
Helps design safer and more efficient circuits
Useful for electronics students and engineers
Reduces human calculation errors
Helps determine correct component ratings
Supports learning of basic electrical principles
Improves troubleshooting efficiency for electrical systems

When & Where to Use

Designing LED circuits with correct resistor values
Calculating power consumption of electronic devices
Troubleshooting faulty electrical circuits
Determining correct resistor ratings for components
Learning electrical engineering concepts
Testing battery-powered circuits
Analyzing Arduino or microcontroller projects
Evaluating electrical loads in small devices

Who Should Use This Calculator

The Ohm’s Law Calculator is designed for a wide range of users including students, engineers, electricians, technicians, and electronics hobbyists.

Students studying physics or electronics can use the calculator to better understand how electrical quantities interact in a circuit.

Electrical engineers frequently rely on Ohm’s Law when designing power systems, electronic devices, and circuit boards.

Electricians use Ohm’s Law to diagnose wiring problems, calculate electrical loads, and ensure circuits operate safely.

DIY electronics enthusiasts and hobbyists often use Ohm’s Law when building circuits using components such as resistors, LEDs, sensors, and microcontrollers.

This calculator provides a simple and reliable way to perform these calculations quickly and accurately.