One kilowatt (kW) is exactly 1,000 watts (W). This is a fixed metric prefix conversion defined by the International System of Units (SI), meaning no electrical assumptions (like voltage, phase, or power factor) are required to answer the pure math question. The formula is simply: Watts = Kilowatts × 1,000. Substituting our target value: 1 kW × 1,000 = 1,000 W.
However, on the jobsite or at the workbench, DIYers rarely ask this question just for metric trivia. Usually, you are trying to size a breaker, select a wire gauge, or pick an off-grid inverter for a "1 kW load." While the power remains a fixed 1,000 W, the current (Amps) that 1,000 W draws shifts dramatically depending on your system voltage, phase configuration, and the load's power factor. Below, we break down the pure conversion, explain when the math becomes meaningless, and provide a concrete decision path for sizing your circuit.
The Pure Metric Conversion (±20% Range)
The prefix "kilo" universally denotes a multiplier of one thousand. Whether you are measuring the output of a solar array or the consumption of a microwave, the relationship is linear and absolute. According to the National Institute of Standards and Technology (NIST), the SI prefix table locks this value permanently.
| Kilowatts (kW) | Watts (W) | Common Real-World Equivalent |
|---|---|---|
| 0.8 kW | 800 W | High-end microwave oven |
| 0.9 kW | 900 W | Standard toaster oven |
| 1.0 kW | 1,000 W | Standard portable space heater (low setting) |
| 1.1 kW | 1,100 W | Large window AC unit (cooling) |
| 1.2 kW | 1,200 W | Portable space heater (high setting) |
When "Watts" is the Wrong Question: Voltage, Phase, and Power Factor
If you know your load is 1 kW (1,000 W), the power is fixed. But to protect the circuit, you need to know the Amps. The assumption that fixes the current answer is a combination of Voltage, Phase, and Power Factor (PF).
For purely resistive loads (like a space heater or incandescent bulb), the Power Factor is 1.0, meaning Real Power (Watts) equals Apparent Power (Volt-Amps). Here is how the current draw for a 1,000 W load shifts across common global and residential systems:
- 120V Single-Phase (US/Canada): 1,000 W ÷ 120 V = 8.33 Amps
- 230V Single-Phase (UK/EU/AU): 1,000 W ÷ 230 V = 4.35 Amps
- 208V Three-Phase (US Commercial): 1,000 W ÷ (208 V × √3) = 2.78 Amps
If you are looking at a generator, UPS, or industrial motor rated in kVA (kilovolt-amps) and trying to figure out how many watts it can supply, the conversion is meaningless if the Power Factor (PF) is unknown. The formula is kW = kVA × PF. A 1 kVA UPS with an unknown PF could deliver 1,000 W (if PF=1.0) or just 600 W (if PF=0.6). Never assume PF=1.0 for reactive loads like compressors or pumps; always check the nameplate or size your wire based on the kVA (apparent power) to avoid overheating.
Decision Tree: Sizing Breakers and Wire for a 1 kW (1000W) Load
Use this decision path to select the correct overcurrent protection and wire gauge for a 1,000 W device. This path assumes a standard residential environment and copper conductors.
| Condition / Scenario | Calculation & NEC Rule | Concrete Pick (Breaker & Wire) |
|---|---|---|
| 120V, Non-Continuous (Runs < 3 hours, e.g., a microwave) |
8.33A. No derating required. Standard breaker sizing. | 15A Breaker (e.g., Square D QO115) 14 AWG NM-B |
| 120V, Continuous (Runs 3+ hours, e.g., baseboard heater) |
8.33A × 1.25 (NEC 210.20(A)) = 10.41A. Must round up to next standard breaker. | 15A Breaker (e.g., Square D QO115) 14 AWG THHN |
| 230V, Continuous (UK/EU/AU standard ring/main) |
4.35A × 1.25 = 5.43A. Well within standard minimal circuit limits. | 10A or 16A MCB (Type C) 1.5 mm² or 2.5 mm² Copper |
| Off-Grid 12V DC Inverter (Running a 1000W AC load from batteries) |
1000W ÷ 12V = 83.3A DC. Add 15% inverter inefficiency = 95.8A DC. | 1500W Pure Sine Inverter 2/0 AWG Welding Cable + 125A ANL Fuse |
The NEC 125% Rule: Why 1,000W Trips a 10A Breaker
A common mistake among DIYers is calculating that a 1,000 W heater on a 120V circuit draws 8.33 Amps, and therefore assuming it can safely run on a 10 Amp breaker (since 8.33A < 10A). If that heater runs for three hours or more, it will trip the breaker.
According to the National Electrical Code (NEC) Article 210.20(A), continuous loads must be calculated at 125% of their rated current. The U.S. Department of Energy notes that heating appliances are among the most common continuous loads in residential settings.
The Math: 8.33 Amps × 1.25 = 10.41 Amps.
Because 10.41A exceeds the 10A breaker rating, you must step up to the next standard overcurrent device size, which is 15 Amps. Furthermore, you must ensure the wire ampacity (using the 60°C column for standard NM-B cable) exceeds 10.41A. 14 AWG copper is rated for 15A, making it the minimum legal and safe choice.
FAQ: Kilowatt and Watt Edge Cases
What is the difference between kW and kWh?
A kilowatt (kW) is a measure of power (the rate at which energy is used right now), equal to 1,000 watts. A kilowatt-hour (kWh) is a measure of energy (power multiplied by time). If you run a 1 kW (1,000 W) space heater for exactly one hour, you have consumed 1 kWh of electrical energy. Utility companies bill you in kWh, not kW.
Can I plug a 1 kW device into a standard US 15A outlet?
Yes. A standard US 15A, 120V receptacle can theoretically handle up to 1,800 W (15A × 120V). However, if the 1 kW device is a continuous load (like a space heater left on all night), the 80% NEC derating rule limits the safe continuous draw to 1,440 W. A 1,000 W load is well within this 1,440 W safe continuous limit.
Why does my 1 kW solar inverter say "2000W Surge"?
Inverters and motors deal with two types of power: continuous and surge (peak). A 1 kW (1,000 W) inverter can supply 1,000 W indefinitely. The "2000W surge" rating means it can handle a momentary spike of 2,000 W for a fraction of a second. This is required to start inductive loads like refrigerator compressors or well pumps, which draw 2x to 3x their running wattage for the first few cycles to overcome initial magnetic inertia.
