Ohms Law Calculator
Calculate Voltage, Current, Resistance & Power - Complete Electrical Circuit Calculator
⚡ Pro Tips for Ohms Law Calculations:
Fundamental formula: V = I × R. Power equation: P = V × I. All formulas equivalent: P = I² × R = V²/R. Minimum 2 values required (rest calculated). Always use base units (V, A, Ω, W). Power wheel mnemonic aids memory. Check results using alternate formulas. Unit conversions essential for accuracy.
Ohms Law Calculator - Enter Any 2 Values
✅ Calculation Results:
Power Wheel - All Ohms Law Formulas
The Power Wheel Diagram
P (Power)
Watts [W]
Watts [W]
V
Voltage
(Volts)
Voltage
(Volts)
I
Current
(Amperes)
Current
(Amperes)
R (Resistance)
Ohms [Ω]
Ohms [Ω]
All Equivalent Formulas:
| To Find | Formula 1 | Formula 2 | Formula 3 |
|---|---|---|---|
| Voltage (V) | V = I × R | V = P / I | V = √(P × R) |
| Current (I) | I = V / R | I = P / V | I = √(P / R) |
| Resistance (R) | R = V / I | R = P / I² | R = V² / P |
| Power (P) | P = V × I | P = I² × R | P = V² / R |
How to Use Power Wheel:
The power wheel is mnemonic device showing relationships between V, I, R, P. Cover desired quantity, remaining three show how to calculate it. Example: cover R, see V/I. Three power formulas cover all combinations.
Ohms Law Reference & Examples
Common Electrical Values & Conversions:
| Quantity | Unit | Symbol | Common Values | Conversion |
|---|---|---|---|---|
| Voltage | Volt | V | 120V, 240V, 480V (AC) | 1 kV = 1000 V |
| Current | Ampere | A | 1A, 10A, 100A | 1 mA = 0.001 A |
| Resistance | Ohm | Ω | 100Ω, 1kΩ, 1MΩ | 1 kΩ = 1000 Ω |
| Power | Watt | W | 100W, 1kW, 1MW | 1 kW = 1000 W |
| Energy | Joule | J | 1 J = 1 W × 1 s | 1 kWh = 3,600,000 J |
Practical Calculation Examples:
| Scenario | Known Values | Formula Used | Calculation | Result |
|---|---|---|---|---|
| Household Circuit | 120V, 15A | P = V × I | 120 × 15 | 1800W |
| Heating Element | 240V, 5000W | I = P / V | 5000 / 240 | 20.83A |
| Motor Load | 480V, 10A | R = V / I | 480 / 10 | 48Ω |
| Resistor Heat | 24V, 0.5A | P = I² × R | 0.5² × 96 | 24W |
| Power Dissipation | 5V, 1000Ω | P = V² / R | 5² / 1000 | 0.025W |
Unit Conversion Reference:
Voltage: kV (×1000), V (base), mV (÷1000)
Current: A (base), mA (÷1000), µA (÷1,000,000)
Resistance: MΩ (×1,000,000), kΩ (×1000), Ω (base), mΩ (÷1000)
Power: MW (×1,000,000), kW (×1000), W (base), mW (÷1000)
Current: A (base), mA (÷1000), µA (÷1,000,000)
Resistance: MΩ (×1,000,000), kΩ (×1000), Ω (base), mΩ (÷1000)
Power: MW (×1,000,000), kW (×1000), W (base), mW (÷1000)
⚡ Understanding Ohms Law & Electrical Fundamentals
What is Ohms Law?:
Fundamental principle in electrical engineering. States relationship: \(V = I \times R\) (Voltage equals Current times Resistance). Named after Georg Simon Ohm. Foundation for circuit analysis, power calculations, electrical design. Every electrical circuit obeys this law.
Key Electrical Quantities:- Voltage (V): Electrical potential difference, measured in volts. Pushes current through circuit. Like water pressure in a pipe.
- Current (I): Flow of electric charge, measured in amperes (amps). Represents charge moving per unit time. Like water flow rate.
- Resistance (R): Opposition to current flow, measured in ohms (Ω). All materials have resistance. Like pipe narrowness.
- Power (P): Rate of energy consumption/transfer, measured in watts (W). P = V × I. Determines heat generation, energy usage.
- Voltage: V = I × R = P / I = √(P × R)
- Current: I = V / R = P / V = √(P / R)
- Resistance: R = V / I = V² / P = P / I²
- Power: P = V × I = I² × R = V² / R
- Circuit Design: Determine wire size, component ratings for safe operation
- Safety: Calculate maximum safe current, voltage for equipment
- Energy Efficiency: Determine power consumption, operating costs
- Troubleshooting: Identify circuit faults, component failures
- Equipment Selection: Choose proper breakers, fuses, wire gauges
- Never exceed component power ratings (fire/explosion hazard)
- Heat dissipation critical at high power (cooling required)
- Always include safety margin (2× calculated values)
- AC circuits more complex (power factor, impedance)
- Professional installation recommended for high-voltage systems
❓ Frequently Asked Questions
How do you find resistance if you know voltage and current?
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Using Ohms Law rearranged: R = V / I. Example: 110V circuit with 0.2A current = 110 / 0.2 = 550Ω. Resistance inversely proportional to current. Higher current (same voltage) = lower resistance.
What happens to power when you double the voltage?
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Power increases quadratically: P = V² / R. Doubling voltage = quadruples power (2² = 4). Example: 5V/1000Ω = 0.025W. At 10V/1000Ω = 0.1W (4× more). Critical for component selection.
Why does resistance increase with wire length?
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Formula: R = ρL/A (resistivity × length / area). Longer path = more opposition to current. Doubling length doubles resistance. Must use thicker wire for long runs to minimize voltage drop.
How is power factor different from real power?
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AC circuits only. Apparent power = V × I. Real power = V × I × PF. Power factor (PF) accounts for reactive components. Typical PF = 0.85-0.95. Lower PF = less efficient energy usage. Capacitor banks used for correction.
What's the difference between AC and DC current?
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DC: constant direction, constant magnitude. AC: alternates direction periodically (60 Hz US, 50 Hz Europe). DC simpler for calculations. AC requires accounting for reactance, impedance, power factor. Most homes use AC distribution.
How do you calculate total power in a circuit?
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Depends on circuit configuration. Series circuits: same current through all components, voltages add. Total power = sum of component powers. Parallel circuits: voltage same across all, currents add. Total power = sum of branch powers.
When must you use the power formulas instead of basic Ohms Law?
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Use power formulas when given power and need other values. Examples: P = I² × R (given power and resistance, find current), P = V² / R (given power and resistance, find voltage). All three power equations equivalent, choose based on known values.
What's the significance of 5% voltage drop limit?
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NEC (National Electrical Code) recommends max 5% voltage drop. Beyond 5%: equipment malfunction, heat generation, energy waste. Applies to branch circuits (3%) and feeders (2%). Designer must choose adequate wire size to maintain within limits.