⚡ Watts to Amps Calculator
Convert watts to amps for any voltage. Essential for sizing circuit breakers, extension cords, and electrical panels.
Watts to Amps Formula: I = P ÷ V. This is derived from Ohm's Law and the power equation. For AC single-phase circuits: I = P ÷ (PF × V) where PF is power factor (typically 0.81.0). For AC three-phase circuits: I = P ÷ (?3 × PF × VL). Standard US household voltage is 120V; large appliances use 240V. The UK and Europe use 230V.
📊 Common Watt-to-Amp Reference Table (120V / 240V)
| Appliance | Watts | Amps @ 120V | Amps @ 240V |
|---|---|---|---|
| Light Bulb (LED) | 10W | 0.08A | 0.04A |
| Laptop | 65W | 0.54A | 0.27A |
| Desktop PC | 300W | 2.5A | 1.25A |
| Microwave | 1200W | 10A | 5A |
| Hair Dryer | 1800W | 15A | 7.5A |
| Electric Dryer | 5000W | 41.7A | 20.8A |
| Electric Oven | 8000W | 66.7A | 33.3A |
🔗 Related Calculators
Watts to Amps: Understanding Electrical Power
Converting watts to amps requires knowing the voltage: Amps = Watts ÷ Volts. This comes from the power formula P = V × I (Power = Voltage × Current). For example, a 1,200-watt microwave on a 120V US circuit draws 1,200 ÷ 120 = 10 amps.
Common Appliance Current Draw
Understanding amp draws helps you avoid tripping breakers and plan electrical capacity. Common US household appliances at 120V: Refrigerator (150W) = 1.25A, LED TV (100W) = 0.83A, Laptop (65W) = 0.54A, Microwave (1,200W) = 10A, Hair dryer (1,875W) = 15.6A, Electric oven (5,000W at 240V) = 20.8A.
AC vs. DC Power and Power Factor
For DC circuits, the calculation is straightforward: A = W ÷ V. For AC circuits, real-world power consumption involves a "power factor" (PF) between 0 and 1 that accounts for reactive loads like motors and transformers: Amps = Watts ÷ (Volts × PF). Resistive loads like heaters and incandescent bulbs have a PF of 1.0. Motors and fluorescent lights typically have a PF of 0.8–0.95. Most household appliance calculations use PF = 1 for simplicity.
Circuit Breaker Sizing Rule
The NEC (National Electrical Code) requires that continuous loads not exceed 80% of a circuit breaker's rated ampacity. A 20-amp circuit should carry no more than 16 amps continuously. This is why a 15A circuit can safely serve a 1,500W (12.5A) heater but not two of them simultaneously.
The Watts-Amps-Volts Relationship
Power (watts), current (amps), and voltage (volts) are related by: P = V × I, or equivalently I = P ÷ V. A 1,200W microwave on a 120V circuit draws 1,200 ÷ 120 = 10 amps. The same appliance in Europe on a 230V circuit would draw 1,200 ÷ 230 = 5.2 amps — the same wattage, but much less current because of the higher voltage. This is why European countries can use thinner wiring for equivalent appliances. When multiple appliances share a circuit, their amperage draws add up — a 15A circuit breaker can safely carry only about 12A continuously (80% rule) before risk of overheating. Knowing wattage and voltage lets you determine if you can safely add another device to an existing circuit.
AC vs DC Power: When Calculations Differ
For DC circuits and purely resistive AC loads (incandescent bulbs, space heaters), P = V × I is exact. For AC circuits with inductive or capacitive loads (motors, transformers, fluorescent ballasts), the relationship involves power factor (PF): P_real = V × I × PF. Power factor ranges from 0 to 1.0 — a perfectly resistive load has PF = 1.0; a motor might have PF = 0.7–0.9. Utilities charge industrial customers for apparent power (kVA = V × I), not just real power (kW = V × I × PF), when PF is low. For home electrical calculations, PF is typically close enough to 1.0 that the simple P = V × I formula works. For motor loads, nameplate current (amps) is always more accurate than calculating from watts alone.
Common Appliance Wattages and Circuit Planning
Planning circuits requires knowing approximate wattages: hair dryer 1,200–1,875W; electric kettle 1,000–1,500W; microwave 600–1,200W; toaster 800–1,800W; refrigerator 100–800W (highly variable, starting surge can be 3× running watts); dishwasher 1,200–2,400W; clothes dryer (electric) 4,000–6,000W (requires 240V, 30A circuit); air conditioner (window unit) 500–1,500W; electric vehicle charger (Level 2) 3,800–9,600W (requires dedicated 240V circuit). The starting surge of motors (refrigerators, AC units) can be 3–7× their running wattage for the first 1–3 seconds — circuit breakers are designed to tolerate brief surges, but UPS systems and generators must be sized for the starting load, not just the running load.
