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W
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V
120V = standard U.S. outlet · 240V = dryer/EV · 12V = automotive
For DC or purely resistive loads, use 1.0
Watts
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| Unit | Symbol | Value | Notes |
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Sources & Methodology
Conversion factors from NIST (National Institute of Standards and Technology) SI unit definitions and IEEE standard electrical quantities. April 2026.
NIST Special Publication 330 — The International System of Units (SI)
Authoritative source for SI unit definitions including the watt (W = kg·m²·s³), joule, and all derived power units used in this converter.
IEEE Standards — Electrical Unit Definitions
IEEE definitions for power factor, apparent power (VA), real power (W), and the mechanical horsepower conversion (1 hp = 745.7 W) used in this calculator.
Conversion factors (from watts):
kW = W / 1,000 | MW = W / 1,000,000 | mW = W x 1,000
HP = W / 745.7 | BTU/hr = W x 3.41214 | J/s = W (identical units)
Amps (DC/resistive) = W / V | Amps (AC) = W / (V x PF) | VA = W / PF
Power factor (PF) accounts for the phase difference between voltage and current in AC circuits. Real power (W) = Apparent power (VA) x PF.
Last reviewed: April 2026 — NIST SI values
How to Convert Watts to Other Power Units
The watt is the SI base unit of power, measuring the rate at which energy is transferred or consumed. Named after Scottish inventor James Watt, it equals one joule per second. Understanding watt conversions is essential for electrical work, energy calculations, HVAC sizing, generator selection, and electricity cost estimation.
W = V x A (DC) | W = V x A x PF (AC) | 1 W = 1 J/s
Common conversions at a glance:
1,000 W = 1 kW • 1,500 W = 1.5 kW • 1 W = 3.412 BTU/hr
1 HP = 745.7 W • 1 kW = 1.341 HP • 1 MW = 1,000 kW
To run a 2,000W appliance on a 120V circuit: 2,000 / 120 = 16.7 amps (PF=1)
1,000 W = 1 kW • 1,500 W = 1.5 kW • 1 W = 3.412 BTU/hr
1 HP = 745.7 W • 1 kW = 1.341 HP • 1 MW = 1,000 kW
To run a 2,000W appliance on a 120V circuit: 2,000 / 120 = 16.7 amps (PF=1)
Watts to Amps: Why Voltage Matters
The same wattage draws very different amperage at different voltages. A 1,000-watt appliance draws 8.33 amps on a 120V circuit but only 4.17 amps on a 240V circuit. This is why high-power appliances like dryers (5,000W) and EV chargers are wired to 240V circuits — the higher voltage halves the current, allowing smaller wire gauges.
| Watts | At 120V (amps) | At 240V (amps) | At 12V (amps) |
|---|---|---|---|
| 100W | 0.83 A | 0.42 A | 8.33 A |
| 500W | 4.17 A | 2.08 A | 41.7 A |
| 1,500W | 12.5 A | 6.25 A | 125 A |
| 5,000W | 41.7 A | 20.8 A | 417 A |
Watts vs Kilowatt-Hours (kWh) — Power vs Energy
Watts measure power (rate of energy use). Kilowatt-hours measure energy (total consumption over time). A 100-watt light bulb running for 10 hours consumes 1 kWh. Your electricity bill charges per kWh, not per watt. To calculate daily energy cost: Power (kW) × Hours × Rate ($/kWh) = Cost. At $0.15/kWh, running a 1,500W space heater 8 hours costs 1.5 × 8 × 0.15 = $1.80/day.
Typical Power Consumption by Appliance
| Appliance | Typical Watts | kW | HP Equivalent |
|---|---|---|---|
| LED bulb | 8–15W | 0.01–0.015 | 0.01–0.02 |
| Laptop | 30–90W | 0.03–0.09 | 0.04–0.12 |
| Refrigerator | 100–400W | 0.1–0.4 | 0.13–0.54 |
| Window AC (1 ton) | 900–1,440W | 0.9–1.44 | 1.2–1.9 |
| Electric dryer | 5,000–7,500W | 5–7.5 | 6.7–10 |
| EV charger (L2) | 7,200–11,500W | 7.2–11.5 | 9.7–15.4 |
💡 Generator sizing tip: Add up the running watts of everything you want to power simultaneously. Then add the highest starting surge wattage (motors typically surge 2 to 3x running watts at startup). Size your generator to at least 1.25x the total running watts plus the largest motor surge. For a whole-home standby, typical residential generators run 10,000 to 22,000 watts.
Frequently Asked Questions
Divide by 1,000. kW = W / 1,000. So 2,500 watts equals 2.5 kilowatts. To convert kilowatts to watts, multiply by 1,000. Kilowatts are used for larger appliances, electric vehicles, solar systems, and utility billing where individual watt figures become unwieldy.
Amps = Watts / Volts (DC or resistive). For AC circuits: Amps = Watts / (Volts x Power Factor). For 1,000W on a 120V circuit at PF=1: 1,000 / 120 = 8.33 amps. The same 1,000W on 240V draws only 4.17 amps. Always know the voltage before calculating current draw.
HP = Watts / 745.7. Example: 1,500 watts / 745.7 = 2.01 horsepower. To convert HP to watts: Watts = HP x 745.7. Electric horsepower used for motor ratings equals 746 watts. Metric horsepower (CV or PS) equals 735.5 watts. Boiler horsepower (for steam) equals 9,810 watts.
The watt is the SI unit of power, measuring the rate of energy transfer. One watt equals one joule per second. In electrical terms: W = V x A (DC). The watt measures how fast a device consumes energy, not the total energy used. A 100W bulb consumes energy twice as fast as a 50W bulb but not necessarily twice as much total energy over a day.
BTU/hr = Watts x 3.41214. Example: 1,000 watts x 3.41214 = 3,412 BTU/hr. To convert BTU/hr to watts: divide by 3.41214. This conversion is used for HVAC, air conditioners, heat pumps, and water heaters where capacity is rated in BTU/hr. A 12,000 BTU/hr AC equals about 3,517 watts (1 ton of cooling).
A kilowatt-hour (kWh) is a unit of energy, not power. 1 kWh = 1,000 watts running for 1 hour. A 100W bulb running 10 hours uses 1 kWh. Your electricity bill is charged in kWh. To estimate cost: Power (kW) x Hours x Rate ($/kWh). At $0.15/kWh, a 500W device running 8 hours costs 0.5 x 8 x 0.15 = $0.60.
W = mW / 1,000. Example: 500 milliwatts / 1,000 = 0.5 watts. To convert watts to milliwatts: mW = W x 1,000. Milliwatts are used for small electronics, radio transmitters, Bluetooth and Wi-Fi signals, optical power, and medical devices where power levels are in the thousandths of a watt range.
Watts = real power (useful work). VA = apparent power (voltage x current regardless of phase angle). In DC circuits they are equal. In AC circuits with motors, transformers, or capacitors, watts are less than VA due to the power factor. Power Factor = W / VA. UPS systems are rated in VA to accommodate different load types with varying power factors.
Highest wattage appliances: electric clothes dryer (5,000 to 7,500W), electric oven range (2,000 to 5,000W), central AC (2,000 to 5,000W), electric water heater (4,000 to 5,500W), electric vehicle charger Level 2 (7,200 to 11,500W). Understanding wattage helps size generators, solar systems, and calculate electricity costs accurately.
The average U.S. home uses approximately 1,200 to 1,500 watts continuously (about 10,500 kWh per year). During peak demand multiple appliances may draw 5,000 to 15,000 watts simultaneously. Whole-home standby generators are typically 10,000 to 22,000 watts to handle peak loads. Solar systems are sized based on average kWh consumption, not peak wattage demand.
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