Watt to Amp Calculator
Convert watts to amps for DC and AC electrical circuits. Calculate current draw and get wire size recommendations based on power, voltage, and current type.
Enter the power consumption in watts
Common voltages: 120V (US household), 240V (US appliances), 230V (EU)
Most household circuits are AC Single Phase
Optional: Default 0.8 for AC. Range: 0-1 (1 = ideal)
How do I convert watts to amps?
For DC or AC single phase: Amps = Watts ÷ Volts. Example: 1200W ÷ 120V = 10A. For AC with power factor: Amps = Watts ÷ (Volts × Power Factor). Example: 1200W ÷ (120V × 0.8) = 12.5A. For AC three phase: Amps = Watts ÷ (√3 × Volts × Power Factor). Power factor accounts for the phase difference between voltage and current in AC circuits, typically 0.8-0.95 for most appliances.
What voltage should I use for my calculation?
Common voltages by region and application: US residential outlets: 120V (standard), 240V (dryer, stove, AC). EU/UK residential: 230V. Automotive: 12V DC (cars), 24V DC (trucks). Industrial: 208V, 277V, 480V (three phase). Check your device nameplate or outlet type. US 120V outlets have two vertical slots; 240V have different configurations (L-shaped, perpendicular slots). Always verify actual voltage with a multimeter for critical applications.
What is power factor and when do I need it?
Power factor (PF) is the ratio of real power (doing work) to apparent power (total power) in AC circuits. Range: 0 to 1 (1 = most efficient). Typical values: Resistive loads (heaters, incandescent lights): PF = 1.0. Inductive loads (motors, transformers): PF = 0.6-0.8. Electronics (computers, LED lights): PF = 0.5-0.9. Mixed household circuits: PF ≈ 0.8-0.9 (use 0.8 for conservative estimate). Low PF means higher current needed for same power, requiring larger wires and circuit breakers.
How many amps does a typical household appliance draw?
Common appliance amp draws at 120V: LED bulb (10W): 0.08A. Laptop (50W): 0.4A. Coffee maker (1000W): 8.3A. Microwave (1200W): 10A. Hair dryer (1500W): 12.5A. Space heater (1500W): 12.5A. At 240V: Electric range (12000W): 50A. Central AC (3600W): 15A. Electric dryer (5400W): 22.5A. Water heater (4500W): 18.75A. Most household circuits are 15A or 20A - avoid exceeding 80% capacity (12A on 15A circuit, 16A on 20A circuit).
What wire size do I need for my amp calculation?
Wire gauge (AWG) for copper wire, 60°C rated: 14 AWG: up to 15A (most 15A circuits). 12 AWG: up to 20A (most 20A circuits, recommended for 15A). 10 AWG: up to 30A. 8 AWG: up to 40A. 6 AWG: up to 55A. 4 AWG: up to 70A. Use next larger size for: long runs (>50 ft add 20% capacity), hot environments, continuous loads (>3 hours, use 125% of calculated amps). Always consult National Electrical Code (NEC) or local codes. Aluminum wire requires larger gauge for same ampacity.
Can I add multiple devices on one circuit?
Calculate total amps: Add watts of all devices, divide by voltage. Example at 120V: Microwave (1200W) + Coffee maker (1000W) = 2200W ÷ 120V = 18.3A. This exceeds typical 15A circuit (should stay under 12A continuous). Safe practice: Do not exceed 80% of circuit breaker rating. 15A circuit: max 12A (1440W at 120V). 20A circuit: max 16A (1920W at 120V). Dedicated circuits needed for: major appliances (refrigerator, microwave, dishwasher), high-draw devices (space heaters, power tools), or per electrical code.
What is the difference between AC and DC current calculations?
DC (Direct Current): Simple calculation: Amps = Watts ÷ Volts. Constant voltage and current flow in one direction. Examples: batteries, solar panels, car electrical systems, DC power supplies. AC (Alternating Current): Must account for power factor: Amps = Watts ÷ (Volts × PF). Voltage and current oscillate (60Hz in US, 50Hz in EU). Examples: household outlets, grid power. AC single phase: most residential. AC three phase: industrial, large motors, more efficient for high power. Key difference: AC requires power factor because voltage and current may be out of phase in inductive/capacitive loads.