What Size Power Station Do I Need? A Simple Way to Calculate It

Buying a power station that is too small is the most common mistake we see. Buying one that is far too big is the second. The good news: you only need three numbers to get it right.

The three numbers that matter

Number	Unit	What it decides
Capacity	watt-hours (Wh)	How long your devices can run
Continuous output	watts (W)	How many devices can run at the same time
Surge output	watts (W)	Whether motors (fridges, pumps, AC) can start

1. Capacity: add up your watt-hours

For each device, multiply its watts by the hours you’ll use it per day:

Device watts × hours per day = watt-hours

Then add them up, and divide by 0.85. Power stations lose roughly 10–15% converting battery power to wall-style AC power, so a “1,000 Wh” unit really delivers about 850 Wh to AC devices.

Example — a short power outage:

Device	Watts	Hours	Wh
Refrigerator (compressor runs ~8 h/day)	150	8	1,200
Wi-Fi router + modem	15	24	360
Phones (×2)	10	2	20
LED lights	40	5	200
Total			1,780

1,780 Wh ÷ 0.85 ≈ 2,100 Wh for one day. Add a 20% safety margin and you’re looking at a 2,000–2,500 Wh class power station.

2. Continuous output: add up the watts running at once

Add the watts of everything that could run at the same time. In the example above that’s 150 + 15 + 20 + 40 = 225 W — easy for almost any mid-size unit. But plug in a 1,100 W microwave and you need well over 1,300 W of output.

3. Surge: check anything with a motor

Fridges, freezers, sump pumps and air conditioners draw 3–5× their running watts for a second when the motor starts. A fridge that runs at 150 W can spike to over 1,000 W. Make sure the power station’s surge rating covers your biggest motor plus everything else that’s running.

Quick sizing by use

What you want to do	Capacity to look for	Output to look for
Phones, laptops, camera batteries	250–500 Wh	300 W
CPAP for 1–2 nights (no humidifier)	500–1,000 Wh	300 W+
Car camping with a 12 V fridge	500–1,000 Wh + solar	500 W+
Keep a fridge + essentials on for a day	1,500–2,500 Wh	1,500 W+
Sump pump, well pump, multi-day outages	3,000 Wh+, expandable	3,000 W+ and 240 V option

Other specs worth checking

• Battery chemistry: LFP (LiFePO4) lasts several times more charge cycles than NMC and is the better choice for home backup. NMC is lighter.
• UPS / pass-through switchover: if you want it to protect a CPAP, router or PC during an outage, look for a switchover time of 20 ms or less.
• Expandability: some units accept extra batteries later. That’s often cheaper than buying a giant unit up front.
• Solar input: solar panels typically deliver around 70–80% of their rated watts in good sun. Higher solar input (in watts) means faster recharging during a long outage.
• Weight: anything over about 50 lb needs wheels or two people.

Skip the math

Use our free power station size calculator: tick your devices, adjust hours, and it tells you the capacity, output and surge you need — and which models fit.