What size power station do I need?

By PortablePowerCalc Editorial Team · Updated 2026-11-04 · 9 min read

The short answer: add up the watt-hours your devices use, divide by about 0.85 for inverter losses, and add a 20% cushion. That gives you the capacity. Then check the inverter can handle everything you'll run at once. Here's the full method.

Power station marketing tends to lead with the capacity number in big type, such as "2,048 Wh!", and leave you to work out whether that's enough for your fridge. It's a fair question, and the answer depends almost entirely on what you plan to plug in and for how long. The good news is that the math is simple once you split it into steps.

If you'd rather skip ahead, our power station size calculator does every step below automatically.

Step 1: List what you actually need to run

Be specific and a little ruthless. "Everything in the kitchen" is how people end up shopping for a whole-home battery. Write down the essentials for your situation:

• Power outage: refrigerator, a few lights, phone charging, Wi-Fi router, perhaps a CPAP or a sump pump.
• Car camping: 12 V cooler, phones, a camera battery, string lights, maybe a fan.
• RV or van: fridge, water pump, fan, laptop, lights, and occasionally something big like a coffee maker or microwave.

Step 2: Find each device's watts

Look on the device label, the power brick or the manual. You're looking for a number in watts (W). If the label only shows volts and amps, multiply them: a device rated 120 V and 0.5 A draws up to about 60 W. Labels show maximum draw, so real use is often lower.

For anything that cycles on and off, like fridges, freezers and heated blankets, the label number is misleading on its own. A plug-in watt meter (the kind that sits between the wall socket and the appliance) measures what the device actually uses over a day. It's the single most useful tool for this job, and inexpensive.

Step 3: Estimate hours per day and calculate watt-hours

Multiply each device's watts by the hours you'll run it per day. That gives watt-hours (Wh), the unit power station capacity is measured in. If that distinction is fuzzy, our watts vs. watt-hours guide clears it up in a few minutes.

Notice how lopsided this is. The fridge accounts for about 70% of the total. That's typical: one or two appliances usually dominate, so they're where accurate numbers matter most.

Step 4: Convert daily use into the capacity to buy

Two adjustments turn your daily total into a realistic battery size:

1. Losses. Running devices from a power station's AC outlets means converting battery DC to AC, which typically costs 10–15%. Divide by 0.85 for AC loads. If everything runs from USB or 12 V ports, 0.9 is closer.
2. Margin. Batteries lose capacity with age and in cold weather. A 20% buffer covers that and your estimating errors.

For one full day without any recharging, that's a unit around 2,400 Wh or larger. For a weekend outage without solar, multiply by the number of days. That quickly gets expensive, which is why many people pair a mid-size unit with solar panels instead (more on that below).

Step 5: Check the inverter's continuous and surge ratings

Capacity tells you how long. The inverter rating tells you what you can run at the same time. Add up the watts of everything that might run together and leave some headroom: a 25% buffer is a reasonable rule. In the example above, that's 150 + 36 + 20 + 12 = 218 W, so almost any power station can handle it.

The catch is surge. Motors and compressors briefly draw several times their running watts when they start. A fridge that runs at 150 W can pull 450 W or more for a moment at startup. Most power stations list a surge or peak rating well above their continuous rating for exactly this reason. Our guide to running vs. surge watts covers it in detail.

Common sizing scenarios

These are rough planning ranges based on typical devices, not product recommendations. Your own list may land higher or lower.

If a medical device is involved, check the manufacturer's guidance on battery power and confirm the setup works before you depend on it.

Bigger battery or add solar?

Doubling capacity roughly doubles the price. Adding solar panels lets a smaller battery refill itself during the day. As a rough guide, on a day with 4 peak sun hours, 400 W of panels harvests around 1,200 Wh after real-world losses. That's enough to cover much of the outage example above. The solar panel size calculator works this out for your location.

A sensible pattern for many households: buy enough battery to get through one night comfortably, plus enough solar to refill it on a typical day. Before buying panels, check the power station's maximum solar input, both the watts and the voltage range.

Specs worth checking before you buy

• Battery chemistry. LiFePO4 (lithium iron phosphate) units are heavier but are usually rated for many more charge cycles than older NMC-based units, which matters if you'll use the unit often.
• Pure sine wave output. Standard on most reputable power stations today, and what motors and sensitive electronics need.
• Solar input limit (watts and voltage) and whether it supports charging from AC and solar at the same time.
• Pass-through / UPS mode if you want it to take over automatically when grid power drops.
• Expandability: some units accept extra battery packs later, which can be cheaper than buying big up front.
• Weight: a 2,000 Wh unit often weighs 40–60 lb (18–27 kg). Fine for a home, harder for hiking to a campsite.

The quick version

1. List essential devices and their watts.
2. Watts × hours = Wh for each; add them up.
3. Divide by 0.85, add 20%, multiply by days.
4. Make sure continuous output covers everything at once, and surge covers motor startups.
5. Consider solar to shrink the battery you need.

Open the power station size calculator →