What size power station do I need?
Three numbers decide it: how much energy your devices use (Wh), how much power they draw at once (W), and how hard they kick when they start (surge). Here's how to work out all three in about five minutes.
The short answer
| What you want to power | Typical rated capacity | Minimum AC output |
|---|---|---|
| Phones, tablets, a laptop for a day | 250–500 Wh | 300 W |
| CPAP for one night (no humidifier) | 300–500 Wh | 150 W |
| CPAP with heated humidifier, 2 nights | 1,500–2,000 Wh | 300 W |
| Weekend camping: cooler, lights, phones | 1,000–1,500 Wh | 500 W |
| Fridge + router + lights overnight (12 h) | 1,000–1,500 Wh | 1,500 W (with surge) |
| Home essentials for 24 h, no solar | 3,000–4,000 Wh | 2,000 W |
| Well pump, 240 V loads, home circuits | 3,000 Wh+ expandable | 3,500 W+, 240 V |
The formula we use
For each device, multiply its running watts by the hours it will run per day. Motor appliances like fridges only run part of the time, so we multiply by a duty cycle (about 40% for a fridge). Add everything up, multiply by the number of days, then account for conversion losses and a safety margin:
- Efficiency (default 85%). Turning battery DC power into 120 V AC loses roughly 10–20%, and stations hold a small reserve. Charging over USB-C or 12 V DC loses less, so use 90% if most of your load is DC.
- Margin (default 20%). Covers battery aging, cold temperatures (lithium batteries deliver less below freezing) and the gap between label and real-world watts.
- Solar. If you'll recharge, we subtract panel watts × peak sun hours × 75% (real panels rarely hit their rating) for each full day. The battery still has to cover the night, so we never size below about 60% of one day's use.
- Output. Separately, add up the watts of everything that might run at the same time. Your station's continuous AC output should beat that by about 10%.
- Surge. Take your peak running load and add the largest motor's extra startup draw. That's the surge rating to look for.
Worked examples
1. CPAP for two nights
A CPAP without a humidifier at 40 W for 8 hours uses 320 Wh a night. Two nights is 640 Wh. Divided by 0.85 and with 20% margin, that's about 900 Wh. Turn the heated humidifier on (roughly 90 W total) and the same two nights need about 2,000 Wh. That's why many CPAP users run without the humidifier or use the maker's DC cable during outages.
2. Keeping the fridge cold through a 24-hour outage
A full-size fridge runs about 150 W when the compressor is on, roughly 40% of the time: 150 × 24 × 0.4 = 1,440 Wh a day. Add a router (480 Wh), LED lights (200 Wh), two phones (60 Wh) and a laptop (360 Wh) and you're at about 2,540 Wh of energy. With losses and margin, plan for about 3,600 Wh of rated capacity, or about 2,600 Wh if 400 W of panels can top it up in good sun. Output: around 400 W running, but the fridge compressor can briefly pull 1,200 W or more, so look for 1,500 W+ continuous with a real surge rating.
3. Working from home through a blackout
A laptop (60 W), a monitor (30 W) and the router (20 W) for an 8-hour workday is 880 Wh. With losses and margin: about 1,250 Wh. A ~1 kWh unit covers most of a workday; skip the space heater.
Appliance wattage chart
Typical values for U.S. appliances. Your device's label or manual is the best source. Look for "W" or multiply volts × amps.
| Appliance | Running watts | Startup surge | Notes |
|---|---|---|---|
| Phone charging | 5–20 W | none | USB-C is most efficient |
| Laptop | 45–100 W | none | Gaming laptops up to 230 W |
| Wi-Fi router + modem | 15–30 W | none | Runs 24/7 |
| CPAP (no humidifier) | 30–60 W | none | Humidifier adds 40–80 W |
| LED bulb | 8–12 W each | none | |
| Full-size refrigerator | 100–250 W | 800–1,500 W | ~1–2 kWh/day |
| Chest freezer | 80–150 W | 600–1,000 W | Cycles less than a fridge |
| TV (50" LED) | 70–120 W | none | |
| Microwave | 1,000–1,500 W | brief | Rated cooking watts are lower than draw |
| Coffee maker | 800–1,200 W | none | Short bursts |
| Window AC (5,000 BTU) | 400–550 W | 1,200–1,600 W | Big energy user |
| Sump pump (1/3 HP) | 700–900 W | 1,800–2,200 W | Surge is the limit |
| Well pump (1/2–1 HP, 240 V) | 1,000–2,000 W | 3,000–6,000 W | Needs 240 V output |
| Space heater | 750–1,500 W | none | Drains a 2 kWh battery in 1–3 hours |
Common sizing mistakes
- Buying on capacity alone. A big battery with a 1,000 W inverter still can't run a 1,200 W microwave.
- Trusting "lifting power" for motors. Lifting modes reduce voltage so heaters and kettles run slower. They don't give a fridge or pump the surge it needs to start.
- Forgetting the 24/7 loads. A 20 W router uses 480 Wh a day, as much as a small power station.
- Assuming full solar output. A 200 W panel typically delivers 120–160 W in good sun, and much less in winter or shade.
- Ignoring weight. Units over 2 kWh often weigh 50–100 lb. If you'll carry it, check the listing.
Run your own numbers
Same formula as above. Edit any wattage or hours.