Watt Calculator
Convert electrical potential (Volts) and current (Amps) into real electrical power (Watts) and apparent power (Volt-Amperes). Crucial for checking circuit breaker limits and sizing home generators.
Line RMS voltage (120V US, 230V EU/UK standard)
Continuous or peak operating current in Amperes
1.0 for resistive heating/lights; 0.8–0.9 for motors and compressors
Active electrical power performing useful work
How to Use This Calculator
- Enter line operating voltage (e.g. 120V or 240V).
- Input the equipment current rating in Amperes.
- Adjust power factor (1.0 for resistive heaters, 0.85 for electric motors).
- Read instantaneous power in Watts and Kilowatts.
Formula & Calculation Methodology
Real active power in Watts is voltage multiplied by current and power factor. Apparent power in Volt-Amperes is the simple product of RMS voltage and current.
Worked Example
Standard 120V 15A Kitchen Microwave
240V Air Conditioner Motor with 0.85 PF
Frequently Asked Questions
How many watts can a standard 15A circuit breaker handle?↓
A 120V 15A breaker handles up to 1,800 Watts peak, or 1,440 Watts continuous (80% NEC safety rule).
What is the difference between Watts and Volt-Amperes?↓
Watts represent real power dissipated as work or heat, while Volt-Amperes represent apparent power in AC circuits.
What is a typical power factor for household appliances?↓
Resistive heaters and incandescent bulbs have a 1.0 PF; refrigerators and AC units typically run between 0.80 and 0.90 PF.
How do I convert watts to kilowatt-hours (kWh)?↓
Multiply watts by operating hours and divide by 1,000 (e.g., 1,000 Watts for 2 hours = 2 kWh).
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Source Citation & Disclaimer
Informational tool only; not licensed tax, legal, or financial advice.