What size power station do you need? Watt-hours and watts, worked out

The two numbers

Watt-hours (Wh): how long it lasts. Add up how much you use in a day, multiply by the days you want to cover, and divide by 0.85. The 0.85 is because about 15% is lost turning battery power into wall-outlet power, so a 1,024 Wh station gives you about 870 Wh.

Watts (W): what it can run. The station's output rating has to cover everything running at once, and its surge rating has to cover the biggest motor starting (a fridge, a pump, an air conditioner). If you're new to the difference, kW vs kWh explains it in two minutes.

How much a day

What you run	Per day	Watts to start
Refrigerator	1–2 kWh	about 1,200 W
Chest freezer	0.5–1 kWh	about 800 W
CPAP (a night)	0.3–0.7 kWh	about 100 W
Starlink	0.5–1.5 kWh	about 100 W
WiFi router	0.1–0.3 kWh	about 14 W
Laptop	0.1–0.4 kWh	about 70 W
Window AC	3–8 kWh	about 2,000 W
Space heater	6–18 kWh	about 1,500 W

Worked examples

A one-day outage: fridge, router and laptop. About 1.2–2.7 kWh a day, so 1.4–3.2 kWh of station after losses. A 2 kWh station (like the DELTA 2 Max, about 1,740 Wh usable) covers a full day at the low end and most of one at the high end; a 1 kWh station keeps the fridge cold for roughly 10–21 hours on its own.

A CPAP for a weekend away. Two nights at 0.3–0.7 kWh is 0.6–1.4 kWh, or 0.7–1.6 kWh of station. A 1 kWh station works without the heated humidifier; with it, go bigger or bring a folding panel.

A window AC through a hot afternoon. The station needs about 2,000 W of surge to start it and 500–1,000 W to keep it running. At 3–8 kWh a day, even a 4 kWh station (DELTA Pro 3) lasts roughly 10–28 hours. That's why home backup moves to rack batteries.

What the common sizes look like

Station	Battery	Runs	Starts	240V
EcoFlow DELTA 2	1,024 Wh	1,800 W	2,700 W	no
Jackery Explorer 1000 Plus	1,264 Wh	2,000 W	4,000 W	no
EcoFlow DELTA 2 Max	2,048 Wh	2,400 W	4,800 W	no
Anker SOLIX F3800	3,840 Wh	6,000 W	9,000 W	yes
EcoFlow DELTA Pro 3	4,096 Wh	4,000 W	8,000 W	yes

Specs from each maker's manual or product page. Every one of these runs a fridge; the appliance pages show the hours, like a fridge on a DELTA 2.

When a power station is the wrong size altogether

Past about 4 kWh, or for anything you'd run every day, a small solar system with a rack battery costs less per kWh and grows with you. Power station vs generator vs solar compares the three for outages.

Run your own numbers with the power station runtime calculator, or answer three questions in the emergencies and camping guide.