Ohm's Law Calculator

Calculate voltage, current, resistance, and power

Ohm's Law

Ohm's Law is fundamental to electrical engineering, describing the relationship between voltage, current, and resistance.

Key Uses

• Circuit analysis and design

• Component sizing and selection

• Power calculations

• Safety considerations

About Ohm's Law

Ohm's Law describes the fundamental relationship between voltage, current, and resistance in electrical circuits.

It states that voltage equals current times resistance (V = I × R), forming the foundation of electrical engineering and circuit analysis.

This law was formulated by German physicist Georg Simon Ohm in 1827 and remains one of the most important principles in electronics.

Key Relationships

• V = I × R (Voltage = Current × Resistance)

• I = V / R (Current = Voltage / Resistance)

• R = V / I (Resistance = Voltage / Current)

• P = V × I (Power = Voltage × Current)

• P = I² × R (Power = Current² × Resistance)

• P = V² / R (Power = Voltage² / Resistance)

Ohm's Law Wheel

Ohm's Law Wheel showing relationships between Voltage (V), Current (I), Resistance (R), and Power (P)

By Per Mejdal Rasmussen - Own work, inspired by Teaching Ohm's Law to Techs by Daniel Sullivan, CC BY-SA 3.0, Link

How to Use the Ohm's Law Wheel

The Ohm's Law wheel is a visual reference tool that helps you quickly find the right formula for any electrical calculation.

To use it: Cover the unknown quantity (V, I, R, or P) with your finger or thumb, and the remaining visible formulas will show you how to calculate it.

For example, if you want to find voltage (V), cover the V in the center, and you'll see the formulas I×R, √(P×R), and P/I around it.

💡 Tip: This wheel includes all 12 possible formulas for calculating voltage, current, resistance, and power using Ohm's Law and the power equations.

Ohm's Law Wheel image: Wikipedia - Ohm's Law

Common Applications & Use Cases

Circuit Design

  • • LED current limiting resistors
  • • Voltage divider circuits
  • • Component selection
  • • Load calculations

Power Analysis

  • • Power consumption calculations
  • • Heat dissipation analysis
  • • Battery life estimation
  • • Efficiency measurements

Safety & Troubleshooting

  • • Component ratings verification
  • • Fault diagnosis
  • • Safety calculations
  • • Performance optimization

Practical Examples

Example 1: LED Circuit

Problem: Calculate the resistor needed for a 3.3V LED with 20mA current from a 5V supply.

Solution:

• Voltage across resistor: 5V - 3.3V = 1.7V

• Using R = V / I: R = 1.7V / 0.02A = 85Ω

• Use standard 100Ω resistor (closest higher value)

Example 2: Power Calculation

Problem: Find the power dissipated by a 1kΩ resistor with 12V across it.

Solution:

• Using P = V² / R: P = (12V)² / 1000Ω

• P = 144 / 1000 = 0.144W = 144mW

• A 1/4W (250mW) resistor would be adequate

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