Ohm's Law Explained: Voltage, Current, and Resistance Made Simple

Ohm's Law is the foundation of electronics and electrical engineering. Named after German physicist Georg Ohm, it describes the fundamental relationship between voltage, current, and resistance.

The Ohm's Law Formula

V = I × R

Where:

• V = Voltage (volts)
• I = Current (amperes)
• R = Resistance (ohms, Ω)

The formula can be rearranged to find any value:

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

Simple Examples

Example 1: Finding Voltage

A circuit has 2A of current flowing through a 10Ω resistor. What's the voltage?

V = 2A × 10Ω = 20V

Example 2: Finding Current

A 9V battery is connected to a 30Ω resistor. How much current flows?

I = 9V ÷ 30Ω = 0.3A (300mA)

Example 3: Finding Resistance

A device runs on 120V and draws 5A. What's its resistance?

R = 120V ÷ 5A = 24Ω

Power Formula

P = V × I

Power (measured in watts) can also be found using:

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

*Example: 20V × 2A = 40W

Practical Applications

Ohm's Law is used everywhere:

• Choosing resistors for LED circuits
• Determining wire sizes for electrical installations
• Troubleshooting electronics — measuring voltage drops
• Designing power supplies — matching voltage and current ratings
• Battery selection — ensuring devices get the right power

Try Our Ohm's Law Calculator

Our Ohm's Law Calculator lets you:

• Enter any two values (voltage, current, resistance)
• Instantly calculate the third value
• Also see power consumption
• Perfect for students, hobbyists, and professionals

💡 Remember: Ohm's Law only applies to ohmic materials (where resistance is constant). Some components like diodes and LEDs don't follow Ohm's Law linearly.

*Calculate voltage, current, or resistance with our free Ohm's Law Calculator.*