Ohm's Law Calculator

Welcome to the Ohm's Law Calculator, a comprehensive tool for electrical calculations. Whether you're an electronics hobbyist, student, or professional engineer, this calculator helps you quickly determine voltage, current, resistance, or power by entering just two known values.

Understanding Ohm's Law

Ohm's Law is one of the most fundamental principles in electrical engineering, discovered by German physicist Georg Simon Ohm in 1827. It describes the relationship between voltage, current, and resistance in an electrical circuit.

Where:

• V (Voltage) - The electrical potential difference, measured in Volts (V)
• I (Current) - The flow of electric charge, measured in Amperes (A)
• R (Resistance) - The opposition to current flow, measured in Ohms (Ω)

The Power Equation

Electrical power represents the rate at which electrical energy is transferred in a circuit. Power is related to voltage, current, and resistance through these formulas:

Where P (Power) is measured in Watts (W).

All Formulas at a Glance

How to Use This Calculator

1. Enter two known values: Fill in any two of the four fields (Voltage, Current, Resistance, Power). Leave the unknown values blank.
2. Click Calculate: Press the calculate button to compute the remaining values.
3. View results: The calculator displays all four values with the calculated ones highlighted in green, along with the formulas used and step-by-step solutions.

Practical Examples

Example 1: LED Circuit

You have a 12V power supply and want to power an LED that requires 20mA (0.02A) of current. What resistance do you need?

• Given: V = 12V, I = 0.02A
• R = V ÷ I = 12 ÷ 0.02 = 600Ω
• P = V × I = 12 × 0.02 = 0.24W

Example 2: Home Appliance

A 100W light bulb operates at 120V. What current does it draw?

• Given: P = 100W, V = 120V
• I = P ÷ V = 100 ÷ 120 = 0.833A
• R = V² ÷ P = 120² ÷ 100 = 144Ω

Metric Prefixes

Electrical values often span many orders of magnitude. Here are common metric prefixes:

Frequently Asked Questions

What is Ohm's Law?

Ohm's Law is a fundamental principle in electrical engineering that describes the relationship between voltage (V), current (I), and resistance (R). It states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to the resistance. The formula is V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms.

How do I calculate power using Ohm's Law?

Power (P) in watts can be calculated using several formulas derived from Ohm's Law: P = V × I (voltage times current), P = I² × R (current squared times resistance), or P = V² ÷ R (voltage squared divided by resistance). This calculator automatically determines which formula to use based on the values you provide.

What are the units used in Ohm's Law calculations?

The standard units in Ohm's Law are: Voltage (V) measured in Volts (V), Current (I) measured in Amperes (A), Resistance (R) measured in Ohms (Ω), and Power (P) measured in Watts (W). This calculator supports various metric prefixes like milli (m), kilo (k), and mega (M) for convenience.

How many values do I need to enter to use this calculator?

You need to enter at least two known values to calculate the remaining unknowns. For example, if you know voltage and current, the calculator will determine resistance and power. Any combination of two values from voltage, current, resistance, and power will work.

Applications of Ohm's Law

• Circuit Design: Engineers use Ohm's Law to design circuits with proper component values
• Troubleshooting: Technicians diagnose electrical problems by measuring and calculating expected values
• Power Management: Determine power consumption and heat dissipation in electronic devices
• Safety: Calculate appropriate wire gauges and fuse ratings to prevent overheating
• Battery Life: Estimate how long a battery will power a device

Historical Background

Georg Simon Ohm (1789-1854) was a German physicist who discovered the relationship between voltage, current, and resistance in 1827. His work was initially met with skepticism, but eventually became one of the cornerstones of electrical engineering. The unit of resistance, the Ohm (Ω), was named in his honor.

Related Resources

• Ohm's Law - Wikipedia
• Georg Ohm - Wikipedia
• Electric Power - Wikipedia