Does Ohm's Law work for AC circuits?

For AC circuits, Ohm's Law uses impedance (Z) instead of resistance, which includes capacitive and inductive reactance. This calculator is designed for DC and purely resistive AC circuits.

How do I calculate resistor power rating?

Calculate the power dissipation using P = I²R or P = V²/R, then choose a resistor rated for at least 2x the calculated power for safety margin.

What is the relationship between the formulas?

All formulas are mathematically equivalent. V = IR can be rearranged to I = V/R or R = V/I. Power formulas P = VI, P = I²R, and P = V²/R all give the same result.

Engineering

Ohm's Law & Power Calculator

Calculate electrical values using Ohm's Law (V=IR) and power equations. Find voltage, current, resistance, or power from any two known values.

What do you want to calculate?

Current

Resistance

Power

Enter any two values to calculate the others

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Calculate Any Electrical Value

Ohm's Law and power equations form the foundation of electrical engineering. Our calculator lets you find any unknown value (voltage, current, resistance, or power) when you know two others.

What is Ohm's Law?

Ohm's Law states that the current through a conductor is directly proportional to the voltage and inversely proportional to the resistance. Combined with power equations, you can calculate any electrical parameter.

Ohm's Law & Power Formulas

V = I × R, P = V × I = I²R = V²/R

Why Use an Ohm's Law Calculator?

Quick Circuit Analysis

Instantly calculate missing values in electrical circuits.

Component Selection

Determine proper resistor values and power ratings.

Safety Calculations

Verify current draw doesn't exceed wire or component ratings.

How to Use the Calculator

Common Applications

LED Circuits

Calculate resistor values for LED current limiting.

Power Supply Design

Determine voltage drop and power dissipation.

Wire Sizing

Calculate current to select appropriate wire gauge.

Battery Life

Estimate runtime from power consumption and capacity.

Frequently Asked Questions

Voltage is measured in Volts (V), current in Amperes (A), resistance in Ohms (Ω), and power in Watts (W). The calculator handles conversions between milli, kilo, and mega prefixes.