Not sure what size power station to buy? Add the devices you want to run, set how many hours a day each one runs, and the calculator gives you the battery capacity (Wh) and output (W) to look for, with real-world losses already included.
Power Station Size Calculator
Add the devices you want to run, how long each one runs per day, and how many days of power you need.
| Device | Watts | Hours / day | Qty |
|---|
Power stations in this size range
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Quick answer
- Capacity (Wh) decides how long it lasts. Add up watts × hours for every device, then add about 35–40% for inverter losses and a safety buffer.
- Output (W) decides what it can run. It must be higher than everything you plug in at once, plus the startup surge of fridges, pumps and AC units.
- Phones, laptops and lights: 300–500Wh is plenty. A fridge through a 1-day outage: about 1,500–3,000Wh. Space heaters and AC: think 3,000Wh+ or a gas generator.
How to use the calculator
- Add your devices. Pick from the list or add a custom device. The watts shown are typical values; for accuracy, check the label on the back of the device or its charger.
- Set hours per day. This is how long the device actually draws power. A fridge plugged in for 24 hours only runs its compressor for about 8 of them, so the list already uses 8.
- Set days of power. Use 1 for a camping weekend you can recharge daily, or 2–3 for an outage with no solar.
- Read the result. Buy a power station at or above the recommended Wh, with continuous output at or above the watts shown.
How the calculation works
The calculator follows the same three steps you would do by hand:
1. Daily energy. Each device’s watts × hours per day × quantity, added together. A 150W fridge running 8 hours uses 1,200Wh; a 15W router running 24 hours uses 360Wh.
2. Conversion losses. Power stations store DC energy and convert it to AC for your wall plugs. That inverter wastes roughly 10–15% as heat, so the calculator divides by 0.85. 1,750Wh of daily use becomes about 2,060Wh of battery.
3. Safety buffer. Batteries lose some capacity with age and cold, and most people do not want to run to 0%. A 20% buffer turns 2,060Wh into about 2,470Wh, which rounds up to the next common size: 3,000Wh.
A big battery with a small inverter cannot run a microwave, and a big inverter with a small battery runs it for only a few minutes. Check both numbers: Wh (how long) and W (how much at once).
Typical power station sizes and what they handle
| Size | Good for | Example runtime |
|---|---|---|
| 300–500Wh | Phones, laptops, lights, CPAP for one night, camera gear | CPAP (40W) about 6–10 hours |
| 700–1,000Wh | Weekend camping, a 12V fridge, short outages, Starlink | Full-size fridge about 12–17 hours |
| 1,500–2,000Wh | Fridge + router + lights through a one-day outage, van life | Full-size fridge about 1–1.5 days |
| 3,000Wh+ | Home backup, power tools, short bursts of microwave or AC | Fridge + essentials about 1.5 days |
Runtimes are estimates using typical appliance draws. Your exact numbers come from the calculator above or the battery runtime calculator.
Startup surge: why fridges and pumps need extra watts
Anything with a motor or compressor (fridges, freezers, sump pumps, window AC, power tools) pulls several times its running watts for a second or two when it starts. A fridge that runs at 150W can spike above 1,000W at startup. Power stations list this as surge or peak watts. The calculator adds the largest startup spike on your list to your running total so you can check the surge rating too.
Tips to get a smaller (cheaper) power station
- Use DC ports when you can. USB-C and 12V outputs skip the inverter, so they waste less energy than AC plugs.
- Avoid heating appliances. Space heaters, kettles and hair dryers use 1,500W. An hour of a space heater uses more energy than a fridge does all day.
- Stagger big loads. If the microwave and coffee maker never run at the same time, you need less output.
- Add solar. Recharging every day means you only need to cover one night, not the whole trip. Plan it with the solar panel size calculator.
Frequently asked questions
What size power station do I need to run a refrigerator?
A typical full-size fridge uses about 1–2kWh per day. For one day of backup, look for at least 1,500–2,000Wh with a surge rating of 1,200W or more. A 1,000Wh unit will usually run it for around 12–17 hours.
Is a 1,000Wh power station enough?
For camping, laptops, lights, a CPAP or a 12V fridge, yes. For a full-size fridge plus other home essentials over a whole day, it is usually too small unless you can recharge it with solar.
What is the difference between Wh and W?
Wh (watt-hours) is how much energy the battery stores, like the size of a fuel tank. W (watts) is how fast it can deliver that energy, like the width of the fuel hose. You need enough of both.
Why is the recommended size so much bigger than my daily use?
Converting battery power to AC wastes about 15%, and the 20% safety buffer covers battery ageing, cold weather and not draining to zero. Together they add roughly 40% on top of your daily use.