Ohm's Law Calculator - Voltage, Current, Resistance & Power
Free online Ohm's Law calculator and electrical power wheel. Calculate Voltage (V), Current (I), Resistance (R), and Power (P) from any two known variables using all 12 primary electrical equations with an interactive visual formula wheel diagram.
Ohm's Law Calculator & Power Wheel
Calculate Voltage (V), Current (I), Resistance (R), and Power (P) with interactive Ohm's law formula wheel.
Select Known Variables
Interactive Ohm's & Joule's Law Formula Wheel
Ohm's Law & Joule's Power Law Guide: Voltage, Current, Resistance & Electrical Power
Ohm's Law and Joule's Law form the bedrock of electrical engineering, circuit analysis, and power electronics. This guide covers the 12 core mathematical formulas connecting Voltage (V), Current (I), Resistance (R), and Power (P).
The 12 Governing Electrical Equations
Voltage Formulas: V = I · R = P / I = √(P · R)
Current Formulas: I = V / R = P / V = √(P / R)
Resistance Formulas: R = V / I = V² / P = P / I²
Power Formulas: P = V · I = I² · R = V² / R
Step-by-Step Instructions
Enter Any Two Known Electrical Values
Input any two parameters among Voltage (`V` in Volts), Current (`I` in Amperes), Resistance (`R` in Ohms), or Power (`P` in Watts).
Select Appropriate Units
Choose standard units or metric sub-units: Millivolts (`mV`), Kilovolts (`kV`), Milliamps (`mA`), Kilohms (`kΩ`), and Milliwatts (`mW`).
Execute Instant Ohm's Law Evaluation
The calculator solves for the remaining two unknown electrical properties with step-by-step mathematical formulas.
Review Interactive Ohm's Law Wheel
Inspect the 12-formula Ohm's Law wheel diagram highlighting the active equation applied for your calculation.
Key Features & Capabilities
- Solves all 12 fundamental Ohm's Law and Joule's Law equations across Voltage (`V`), Current (`I`), Resistance (`R`), and Power (`P`)
- Core formulas: `V = I * R`, `P = V * I`, `P = I^2 * R`, and `P = V^2 / R`
- Dynamic multi-unit support handling microamps (`µA`), milliamps (`mA`), kilohms (`kΩ`), megohms (`MΩ`), and megawatts (`MW`)
- Direct Current (DC) and single-phase AC calculations with true power dissipation factor
- Interactive SVG Ohm's Law formula wheel dynamically illuminating corresponding equations
- Instant laboratory-grade precision with zero server roundtrips
Frequently Asked Questions
What is Ohm's Law and what are its core mathematical formulas?
Ohm's Law states that electrical current flowing through a conductor between two points is directly proportional to voltage and inversely proportional to resistance. The core formulas are: `Voltage (V) = I * R`, `Current (I) = V / R`, and `Resistance (R) = V / I`, where V is in Volts, I is in Amps, and R is in Ohms.
How do you calculate electrical power (Watts) using Ohm's Law?
Electric power (P) in Watts is calculated by combining Ohm's Law with Joule's Law: 1. `P = V * I` (Voltage * Current), 2. `P = I^2 * R` (Current squared * Resistance), 3. `P = V^2 / R` (Voltage squared divided by Resistance).
How do you calculate current if you know a 100W light bulb runs on a 120V circuit?
Using the formula `I = P / V`: `Current = 100 Watts / 120 Volts = 0.833 Amperes`. The light bulb's operating resistance is `R = V / I = 120 / 0.833 = 144 Ohms`.
Does Ohm's Law apply to both AC and DC circuits?
Ohm's Law applies directly to pure DC circuits and purely resistive AC circuits (like heaters and incandescent lights). For AC circuits containing inductors or capacitors, resistance `R` is replaced by total complex impedance `Z` (`V = I * Z`), factoring in phase angle shifts.
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