Electrical Calculator: How to Calculate Voltage, Current, Resistance, and Power for Any Circuit

Understanding the relationship between voltage, current, resistance, and power is essential for anyone working with electronics — whether you are an electrician wiring a building, an engineering student studying circuit theory, or a hobbyist building your own projects. Our free online Electrical Calculator applies Ohm’s Law and the Power Law to give you instant results for any electrical calculation.

Ohm’s Law: The Foundation of Electrical Calculations

Ohm’s Law states that the current flowing through a conductor is directly proportional to the voltage and inversely proportional to the resistance. The formula is simple:

V = I × R

Symbol	Meaning	Unit
V	Voltage (potential difference)	Volts (V)
I	Current (flow of electrons)	Amperes (A)
R	Resistance (opposition to flow)	Ohms (Ω)

Given any two values, you can calculate the third:

• V = I × R — Find voltage
• I = V ÷ R — Find current
• R = V ÷ I — Find resistance

Power Calculations

The Power Law calculates how much energy a circuit consumes:

P = V × I

Where P is power in Watts (W). You can also express power using resistance:

• P = I² × R — Power from current and resistance
• P = V² ÷ R — Power from voltage and resistance

Practical Examples

Example 1: Finding Current

You have a 120V circuit with a 24Ω resistor. What is the current?

I = V ÷ R = 120 ÷ 24 = 5 Amperes

Example 2: Finding Power Consumption

A device draws 2A at 12V. How much power does it consume?

P = V × I = 12 × 2 = 24 Watts

Example 3: Finding Resistance

You measure 9V across a component carrying 0.5A. What is its resistance?

R = V ÷ I = 9 ÷ 0.5 = 18 Ohms

Skip the manual math and use the Electrical Calculator to compute voltage, current, resistance, and power in seconds.

Common Applications

Application	What You Calculate
Choosing a power supply	Required voltage and current for your device
Circuit design	Resistor values to achieve target current
Wire sizing	Current draw to select proper wire gauge
Battery life estimation	Power consumption in watts to estimate runtime
LED resistor selection	Resistor needed to limit current through an LED

Whether you are designing a circuit, troubleshooting an appliance, or learning electronics fundamentals, the Electrical Calculator is your go-to tool for fast, accurate calculations.