Ohm's Law Calculator
Ohm's Law Calculator
Calculate voltage, current, resistance, or power using Ohm's Law and power formulas
Ohm's Law Calculator: Complete Electrical Guide
Ohm's Law states that voltage across a conductor is directly proportional to current through it (V = IR).This fundamental principle of electrical engineering, discovered by Georg Ohm in 1827, forms the foundation for understanding electrical circuits, power calculations, and circuit design.
Our professional Ohm's Law calculator handles all electrical calculations including voltage, current, resistance, and power computations with safety analysis, unit conversions, and circuit classification for electrical engineering, electronics, and electrical safety applications.
Quick Answer
To use Ohm's Law: V = I × R, where V is voltage (volts), I is current (amperes), and R is resistance (ohms). For example, 12V across 100Ω resistance produces I = V/R = 12V ÷ 100Ω = 0.12A (120mA) current. Power dissipated is P = V × I = 12V × 0.12A = 1.44W.
Mathematical Foundation
Ohm's Law: Voltage equals current times resistance
Essential Formulas:
Ohm's Law Variations
V = I × R (Voltage)
I = V / R (Current)
R = V / I (Resistance)
Power Formulas
P = V × I (Power from voltage and current)
P = I² × R (Power from current and resistance)
P = V² / R (Power from voltage and resistance)
Units
V: Volts (V), I: Amperes (A), R: Ohms (Ω), P: Watts (W)
Common prefixes: milli (m), kilo (k), mega (M)
Circuit Classifications
Low Voltage Electronics
Safe for experimentation and learning. Typically < 50V, < 1A, < 1W.
Examples: LED circuits, microcontroller projects
Arduino: 5V, Raspberry Pi: 3.3V
Battery circuits: 1.5V - 12V
Safety: Minimal shock hazardResidential/Commercial
Standard household and office electrical systems.
AC Voltage: 120V (US), 230V (EU)
Typical loads: 100W - 1500W
Circuit protection: 15A - 20A breakers
Safety: Potentially lethal - follow codesHigh Voltage/Industrial
Industrial equipment and high-power applications.
Voltage: > 1000V or Power > 1000W
Motors, transformers, power distribution
Arc flash hazards, specialized protection
Safety: Qualified personnel onlyApplications of Ohm's Law
Circuit Design
Resistor Selection
Calculate required resistance values for current limiting, voltage division, and biasing circuits
Power Ratings
Determine component power requirements and heat dissipation for safe operation
Wire Sizing
Calculate wire gauge requirements based on current capacity and voltage drop
Troubleshooting
Circuit Analysis
Verify circuit operation, identify faulty components, and analyze performance
Load Testing
Determine actual vs. expected power consumption and efficiency measurements
Safety Verification
Ensure circuits operate within safe current, voltage, and power limits
Example Problems with Solutions
Example 1: LED Current Limiting
Design a resistor for a 3.3V LED that needs 20mA from a 5V supply.
Answer: Use 82Ω or 100Ω, 1/8W resistor
Example 2: Household Appliance
A 1500W heater operates on 120V. What current does it draw?
Answer: Current = 12.5A, needs 20A circuit
Example 3: Power Supply Design
Design a 12V power supply to deliver 2A. What's the load resistance?
Answer: Load resistance = 6Ω, 30W supply recommended
Electrical Safety
Voltage Safety
Current Safety
Safety Guidelines
Personal Safety
- • Turn off power before working on circuits
- • Use insulated tools and safety equipment
- • Work with one hand when possible
- • Never work on live high-voltage circuits
Equipment Safety
- • Use proper fuses and circuit breakers
- • Ensure adequate wire gauge for current
- • Provide proper ventilation for heat dissipation
- • Follow electrical codes and standards
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Ohm's Law Calculator
Calculate voltage, current, resistance, or power using Ohm's Law and power formulas