Ohm's Law is a fundamental principle in electrical engineering stating that the current passing through a conductor between two points is directly proportional to the voltage across the two points. The standard formula is V = I × R (Voltage = Current × Resistance).

How do you calculate power using Ohm's Law?

To calculate electrical power (measured in Watts), you combine Ohm's Law with Watt's Law. The most basic formula is Power = Voltage × Current (P = VI). If you don't know the voltage, you can also use Power = Current squared × Resistance (P = I²R).

Can Ohm's law be used for AC circuits?

The basic V=IR formula applies strictly to DC circuits or purely resistive AC circuits. For standard AC circuits containing capacitors or inductors, Ohm's law must be modified to include Impedance (Z) instead of just resistance, becoming V = I × Z.

Engineering Calculators

Ohm’s Law Calculator (Voltage, Current, Resistance & Power Calculator)

Instantly calculate Voltage (V), Current (I), Resistance (Ω), and Power (W) using Ohm’s Law and Watt’s Law. Perfect for electrical engineers, students, electricians, and circuit designers.

QUICK SCENARIOS:

Step 1: Select Two Known Values

Voltage (V)

Current (I)

Live Circuit Status

Voltage (V)

12.00 V

12000.00 mV

Current (I)

2.00 A

2000.00 mA

Resistance (R)

6.00 Ω

6000.00 mΩ

Power (P)

24.00 W

24000.00 mW

📐 Step-by-Step Solution

Ohm's & Watt's Law Triangles

V = I × R

P = V × I

I²R

P = I² × R

Free Ohm's Law Calculator & Watt's Law Calculator

Whether you are an electrical engineering student, a licensed electrician, or a DIY hobbyist, solving electrical circuits requires precision. Our professional Ohm's Law Calculator seamlessly integrates Watt's Law, allowing you to quickly determine Voltage (V), Current (I), Resistance (R), and Power (P) by simply entering any two known variables.

How to Use the Calculator

Select Your Knowns: Use the dropdown menu at the top to select the two electrical parameters you already know.
Enter Your Values: Type your numbers or use the interactive sliders.
Adjust Your Units: Use the adjacent dropdowns to define your metric prefixes. The calculator flawlessly handles milli (m), micro (µ), kilo (k), and Mega (M) conversions instantly.
View Instant Results: Calculated answers are highlighted in green, complete with primary and secondary scaled units. The step-by-step formula breakdown is shown automatically below the results.

Example Calculations

Example 1: Finding Resistance & Power

If a circuit has Voltage = 12V and Current = 2A:

• Resistance: R = V / I ➔ 12 / 2 ➔ 6.00 Ω

• Power: P = V × I ➔ 12 × 2 ➔ 24.00 W

What is Ohm’s Law?

Ohm’s Law states that the current flowing through a conductor is directly proportional to the voltage and inversely proportional to the resistance. Formula: V = I × R. This law is fundamental to electrical engineering and is widely used in circuit analysis, electronics design, and troubleshooting.

Watt’s Law

Watt’s Law defines the relationship between power, voltage, and current. Formula: P = V × I. This is used to calculate total electrical power consumption in circuits and devices, determining how much energy a component uses or generates as heat.

Common Uses of Ohm’s Law

Electrical circuit design and PCB routing
Battery life and load calculations
Sizing the correct LED current-limiting resistor
Estimating power consumption for household appliances
Electrical troubleshooting and multimeter diagnostics

⚠️ Electrical Safety Tip: Always ensure circuits are fully powered off and disconnected before measuring resistance (Ohms) with a multimeter. Measuring resistance on a live circuit can severely damage your testing equipment, cause inaccurate readings, and poses a serious shock hazard.

Educational Disclaimer: The results provided by this calculator represent ideal, theoretical DC circuits. Always consult a licensed professional before working on real-world electrical systems.

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Engineering Calculators

Ohm’s Law Calculator (Voltage, Current, Resistance & Power Calculator)

Instantly calculate Voltage (V), Current (I), Resistance (Ω), and Power (W) using Ohm’s Law and Watt’s Law. Perfect for electrical engineers, students, electricians, and circuit designers.

Ohm's & Watt's Law Triangles

Free Ohm's Law Calculator & Watt's Law Calculator

How to Use the Calculator

Example Calculations

What is Ohm’s Law?

Watt’s Law

Common Uses of Ohm’s Law

💡 Have a suggestion or found a bug?

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