Watts to Amps Calculator
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How do you convert watts to amps?
To convert watts to amps, divide watts by volts. For example, a 1500 W heater on a 120 V circuit draws 1500 ÷ 120 = 12.5 amps; on a 240 V circuit the same 1500 W draws 1500 ÷ 240 = 6.25 A. For AC circuits, also divide by the power factor: A = W ÷ (V × PF).
Watts to Amps Conversion Table (DC)
Watts to Amps Formula
Common Household Loads: What Do They Actually Draw?
Knowing the rated watts of a device is only half the picture — the amp draw determines which circuit, breaker, and extension cord you can safely use. Here are four common household items with their typical wattage ranges and resulting amp draw at 120 V (US standard household voltage), calculated with the DC/purely-resistive formula A = W ÷ V (PF ≈ 1.0 for heating and resistive loads; motors vary).
| Device | Typical rated wattage | Amps at 120 V | Why it matters |
|---|---|---|---|
| Hair dryer (high heat) | 1,500 – 1,875 W | 12.5 – 15.6 A | Fills a standard 15 A bathroom circuit; running anything else on the same circuit risks tripping the breaker. |
| Portable space heater | 750 – 1,500 W | 6.25 – 12.5 A | A 1,500 W heater on a 15 A circuit leaves only 2.5 A of headroom — NEC requires circuits not to be loaded above 80 % continuously, so a dedicated 20 A circuit is strongly recommended. |
| Window air conditioner (5,000 BTU) | 450 – 600 W | 3.75 – 5 A | Fits comfortably on a shared 15 A circuit, but larger units (10,000+ BTU, ~1,000 W) need a dedicated 15 A or 20 A circuit. |
| 10-inch table saw | 1,400 – 1,800 W | 11.7 – 15 A | Starting current (inrush) can be 2–4× rated for a brief moment; a 20 A dedicated circuit and a heavy-duty 12 AWG extension cord (max 25 ft) are standard practice. |
Wattages are manufacturer-typical ranges, not a single model. Always check the device nameplate. At 240 V the amp values halve; use the calculator above for other voltages.
Frequently Asked Questions
Divide the power in watts by the voltage in volts. For DC circuits: A = W ÷ V. For AC single-phase circuits, also divide by the power factor: A = W ÷ (V × PF). For AC three-phase: A = W ÷ (V × PF × 1.732).
DC: A = W ÷ V. AC Single-phase: A = W ÷ (V × PF). AC Three-phase: A = W ÷ (V × PF × 1.732). PF is the power factor — a value between 0 and 1 that accounts for reactive power in AC circuits. DC circuits always have a power factor of 1.
It depends on voltage and circuit type. 120V DC: 12.5 A. 240V DC: 6.25 A. 120V AC single-phase (PF 0.8): 15.625 A. 240V AC single-phase (PF 0.8): 7.8125 A.
Watts (W) measure electrical power — the rate at which energy is consumed or produced. Amps (A) measure electric current — the rate at which electric charge flows through a conductor. The two are linked by voltage: W = A × V. A device can draw few amps at high voltage or many amps at low voltage while consuming the same wattage.
Most bathroom circuits in US homes are 15 A (1,800 W at 120 V). A hair dryer alone draws 12.5–15.6 A on its high-heat setting — leaving almost no room for anything else. The NEC (National Electrical Code) also requires that a circuit not be loaded above 80 % of its rating continuously (80 % of 15 A = 12 A). Exceeding that trips the breaker as a safety measure before wiring overheats. The fix is either to use the dryer's lower-heat setting or to plug it into a different circuit.