Ohm's Law Calculator
Professional electrical engineering calculator for voltage, current, resistance, and power analysis. Supports DC circuits, AC circuits, three-phase systems with comprehensive safety analysis.
Ohm's Law Calculator
Professional electrical calculator for voltage, current, resistance, and power analysis
Circuit Type
⚡
DC Circuit
Direct Current - constant voltage and currentApplications
Electrical Parameters
V
Electric potential difference
A
Electric current flow
Ω
Opposition to current
W
Electrical power
Calculate & Analyze
Circuit Summary
Characteristics:
Constant voltage
Constant current
Simple calculations
Electrical Formulas
Essential electrical engineering formulas for circuit analysis and design calculations.
Ohm's Law (Basic)
Voltage equals current times resistance
V = I × R
Common Applications:
Power Formulas
Electrical power in various forms
P = V × I = I² × R = V² / R
Common Applications:
AC Power (Single Phase)
AC power with power factor consideration
P = V × I × cos(φ)
Common Applications:
Three Phase Power
Three-phase power calculation
P = √3 × VL × IL × cos(φ)
Common Applications:
Circuit Types
Understanding different electrical circuit configurations and their applications.
DC Circuits
Direct current circuits with constant voltage and current flow
Characteristics:
Constant voltage
Constant current
Simple calculations
No frequency considerations
Applications:
Key Formulas:
V = I × R
P = V × I
Energy = P × t
AC Resistive Circuits
Alternating current circuits with purely resistive loads
Characteristics:
Sinusoidal waveforms
In-phase voltage and current
Power factor = 1
No energy storage
Applications:
Key Formulas:
V = I × R
P = V × I
RMS values used
AC Reactive Circuits
AC circuits with capacitive or inductive components
Characteristics:
Phase differences
Reactive power
Power factor < 1
Energy storage elements
Applications:
Key Formulas:
S = V × I
P = S × cos(φ)
Q = S × sin(φ)
Three Phase Systems
Balanced three-phase AC power systems
Characteristics:
Three sinusoidal waveforms
120° phase separation
Constant instantaneous power
Balanced loads
Applications:
Key Formulas:
P = √3 × VL × IL × cos(φ)
S = √3 × VL × IL
Electrical Safety Guidelines
Critical safety information for electrical work. Always prioritize safety and follow proper procedures.
Voltage Safety
Extra Low Voltage (≤50V): Generally safe for direct contact
Low Voltage (50-1000V): Standard electrical safety required
Medium Voltage (1-35kV): Qualified personnel only
High Voltage (>35kV): Expert technicians with specialized equipment
Current Safety
1mA: Threshold of perception for humans
5mA: Maximum safe current for continuous contact
10-20mA: Muscular control lost, cannot let go
50mA: Ventricular fibrillation possible
>100mA: Severe burns and cardiac arrest
Power Safety
Low Power (<100W): Minimal safety concerns
Medium Power (100-1000W): Heat management required
High Power (1-10kW): Professional installation needed
Industrial Power (>10kW): Specialized safety protocols
General Safety
Always de-energize circuits before working
Use proper personal protective equipment (PPE)
Follow lockout/tagout (LOTO) procedures
Test circuits with appropriate instruments
Follow local electrical codes and standards
Electrical Standards
International and regional electrical standards, voltage systems, and safety requirements.
| Region | Standards | Voltages | Frequency |
|---|---|---|---|
International | IEC 60038 - Standard Voltages IEC 60364 - Electrical Installations | 230V/400V (3-phase) 120V/208V 480V/277V | 50Hz/60Hz |
United States | NEC (National Electrical Code) IEEE Standards | 120V/240V (residential) 208V/120V (commercial) 480V/277V (industrial) | 60Hz |
Europe | EN Standards VDE (Germany) | 230V/400V (standard) 110V (construction) 690V (industrial) | 50Hz |
Asia Pacific | AS/NZS (Australia/NZ) JIS (Japan) | 230V/400V (most) 100V/200V (Japan) 220V/380V (China) | 50Hz/60Hz |
Practical Applications
Real-world examples and calculations for common electrical engineering scenarios.
Home Electrical Systems
Calculating circuit breaker requirements
For a 1500W heater on 120V: I = P/V = 1500W/120V = 12.5A, use 15A breaker
Determining wire gauge requirements
For 20A circuit: Use 12 AWG copper wire (rated for 20A continuous)
Power consumption analysis
LED bulb 10W vs incandescent 60W: 6x less energy consumption
Motor Applications
Motor starting current calculation
5HP motor at 480V: Running current ≈ 6.5A, Starting current ≈ 39A (6x FLA)
Power factor correction
Motor with 0.8 PF: Reactive power = P × tan(cos⁻¹(0.8)) = 0.75 × P
Efficiency calculations
90% efficient motor: Input power = Output power / 0.9
Electronic Circuits
LED current limiting resistor
For 3V LED with 20mA: R = (Vsupply - VLED) / I = (12V - 3V) / 0.02A = 450Ω
Power dissipation in resistors
In 100Ω resistor with 1A: P = I²R = 1² × 100 = 100W
Voltage divider calculations
For 12V input with R1=1kΩ, R2=2kΩ: Vout = 12V × (2kΩ/(1kΩ+2kΩ)) = 8V
Calculator Features
Voltage Analysis
Calculate voltage drops, potential differences, and voltage requirements for any circuit configuration.
Current Calculations
Determine current flow, ampacity requirements, and current ratings for electrical components.
Resistance Analysis
Calculate resistance values, impedance, and load requirements for optimal circuit design.
Power Analysis
Compute active, reactive, and apparent power with efficiency and power factor analysis.
Safety Analysis
Comprehensive safety evaluation with voltage classification and protection requirements.
Circuit Types
Support for DC, AC resistive, AC reactive, and three-phase circuit configurations.
Advanced Analysis
Power factor calculations, efficiency analysis, and engineering recommendations.
Educational Content
Comprehensive electrical engineering education with formulas, examples, and standards.
Frequently Asked Questions
What is Ohm’s Law?
Ohm’s Law states that voltage equals current times resistance: V = I × R. Rearranged: I = V/R and R = V/I. A circuit with 12V battery and 4Ω resistance draws 3A of current. This relationship holds for ohmic (linear) components at constant temperature and is the most fundamental relationship in circuit design.
What is the power formula in electronics?
Power P = V × I = I² × R = V²/R. For a 100Ω resistor at 5V: P = 5²/100 = 0.25W. Choose a resistor rated at least 2× the calculated power for reliability. A 0.5W resistor would be minimum for this case — 1/4W is adequate at 0.25W calculated dissipation.
How do resistors combine in series and parallel?
Series: Rₜᵒₜₕₐₗ = R₁ + R₂ + R₃... Each resistor drops a portion of total voltage proportional to its value. Parallel: 1/Rₜᵒₜₐₗ = 1/R₁ + 1/R₂ + 1/R₃... For two equal resistors in parallel: Rₜᵒₜₐₗ = R/2. Parallel combination always yields less than the smallest individual resistor.
What is the difference between AC and DC resistance?
DC resistance is governed by Ohm’s Law and material resistivity. AC circuits have impedance Z = √(R² + X²), where X is reactance. Inductors have inductive reactance Xₗ = ωL (increases with frequency) and capacitors have X℀ = 1/ωC (decreases with frequency). At DC (0 Hz), inductors are short circuits and capacitors are open circuits.
How do I calculate a current-limiting resistor for an LED?
R = (Vₛᵤₚₚₗᵧ − Vᶠₑᴰ) / Iᶠₑᴰ. Example: 5V supply, red LED with 2V forward voltage and 20mA forward current: R = (5 − 2) / 0.02 = 150Ω. Use the next standard resistor value of 150Ω or 160Ω. Always include a current-limiting resistor; running an LED without one will immediately destroy it.