What Size Portable Power Station Do You Need? Watts and Wh Explained

Short answer: a portable power station has two numbers that matter, and you size it for both. Watts (W) are how much it can power at once: add up everything you want running at the same time. Watt-hours (Wh) are how long it lasts: multiply each appliance’s watts by the hours you’ll run it, add them up, and allow for losses. With typical figures from ENERGY STAR certified models, a few lights, a laptop, a fan and a TV for an evening come to about 1,000 Wh; add a full-size fridge for a day and you need about 2,300 Wh before losses. Cooling is where the numbers jump: eight hours of a small window air conditioner need about 4,100 Wh. This works the same in an apartment or a house.

A power station is a battery with an inverter and outlets, charged from a wall outlet, a car or solar panels. If your goal is lower bills rather than backup, that’s a different tool: see what plug-in solar is.

Watts vs. watt-hours: the two numbers on the box

Think of watts as the size of the pipe and watt-hours as the size of the tank.

• Output, in watts. The continuous rating is the most the inverter can supply for as long as the battery lasts. Everything plugged in at once has to fit under it. When a listing says “1,000 W”, check whether that’s the continuous output or the surge, and find the battery’s Wh separately.
• Surge, in watts. A higher rating the inverter can supply for a moment, for motors that draw extra power as they start. Electric motors draw much more power when they first start; the USDA Forest Service’s guide to small generators uses three times the rated wattage as a rule of thumb.
• Capacity, in watt-hours. How much energy the battery holds. A 1,000 Wh station could, in theory, run a 100 W load for 10 hours; in practice you get less, because the inverter uses some of it (more on that below).

Two stations with the same output can last very different times, and the other way round, so check both.

Step 1: list what you want to run, and for how long

Start with what really matters in an outage, not everything in the house. For each item you need its watts and the hours you’d use it. The formula is the one Virginia Cooperative Extension gives for estimating appliance use: watts times hours used per day, divided by 1,000, gives kWh a day (BSE-301). Skip the division and you have watt-hours.

Typical figures, the median of every ENERGY STAR certified model in each group as of November 5, 2026:

Appliance	Typical draw	Based on
LED downlight	13 W	3,237 certified fixtures, input power
Ceiling fan, high speed	31 W	1,201 certified fans
Laptop	65 W	1,080 certified notebooks, the charger’s rated output (real use is usually lower)
50 to 55 inch TV	85 W	32 certified TVs, on-mode power
Window AC, 5,000 to 8,000 BTU/h	517 W	169 certified units, our estimate from cooling capacity and efficiency
Full-size fridge	1,241 Wh a day	2,539 certified freestanding models, annual energy use ÷ 365
Compact fridge	671 Wh a day	1,865 certified freestanding models, annual energy use ÷ 365

Sources: ENERGY STAR open data for downlights, ceiling fans, computers, TVs, room air conditioners and refrigerators. Your own appliances can differ a lot, so use their rating plates when you can: the extension guide notes that most list their watts, or volts and amps, which you multiply to get watts.

A fridge is listed per day because it cycles on and off; it doesn’t draw its running watts all the time. Our guide to how many watts a refrigerator uses explains its running, starting and daily figures.

Step 2: add up the watt-hours, then allow for losses

Not every watt-hour on the label reaches your plugs. The inverter that makes AC power uses some, and a station may hold some charge in reserve. Our power station sizer assumes 85% is usable by default, a rough estimate of ours; the station’s maker may list its own figure, and you should use that if it does. So the capacity to look for is your total watt-hours divided by 0.85.

Step 3: check the output and the surge

Add the watts of everything that could be on at the same time, and leave some headroom so the station isn’t running flat out; the sizer adds 25%, again our estimate. For anything with a compressor or a motor, such as a fridge, a freezer or an air conditioner, the surge rating has to cover its start: about three times its running watts, by the Forest Service’s rule of thumb. If a station’s maker lists the appliances it has been checked with, that’s the better guide.

Worked examples

Each uses the typical figures above and our 85% usable and 25% headroom assumptions. Swap in your own numbers in the sizer.

Scenario	What runs	Energy needed	Capacity to look for	Output to look for
An evening without power	4 LED lights for 5 h, a laptop for 4 h, a ceiling fan for 8 h, a TV for 3 h	1,023 Wh	about 1,200 Wh	about 300 W
A day with the fridge	The same, plus a full-size fridge for 24 h	2,264 Wh	about 2,700 Wh	300 W plus the fridge’s running watts, with surge for its start
A hot evening with AC	A window AC for 8 h	4,136 Wh	about 4,900 Wh	about 650 W, with surge for the compressor

The math, for the first row: 4 × 13 W × 5 h + 65 W × 4 h + 31 W × 8 h + 85 W × 3 h = 1,023 Wh, and 1,023 ÷ 0.85 ≈ 1,200 Wh. Output: 52 + 65 + 31 + 85 = 233 W, plus 25% ≈ 300 W.

The pattern: lights, a laptop and a fan are cheap to keep running. A fridge roughly doubles what you need. Anything that heats or cools empties a station fast: besides the air conditioner, the extension guide lists nameplate ranges of 750 to 1,500 W for a portable heater, 1,200 to 1,875 W for a hair dryer and 750 to 1,100 W for a microwave, so check those against the station’s output before you plug them in. If keeping those running is the goal, a home battery installed by a licensed electrician may fit better than a bigger portable station.

Do you need to power the fridge at all?

For a short outage, maybe not. The FDA says an unopened refrigerator keeps food cold for about 4 hours, and a full freezer holds its temperature for about 48 hours (24 if it’s half full) if the door stays closed (FDA). The CDC gives the same limits and suggests moving refrigerated perishables into a cooler with ice once the power has been out for 4 hours (CDC). If outages where you live are usually short, a smaller station for lights and a laptop, plus a cooler, may be all you need instead of one sized for the fridge.

Safety: what a power station is, and isn’t, for

• Look for a lab listing. UL 2743 is UL’s standard for portable power packs, the category power stations fall into: portable or movable packs with internal batteries that power appliances on site, including integral options such as inverters (UL 2743 scope). UL Solutions describes them as charged from an external source and meant for when grid power isn’t available, such as camping or emergencies (UL Q&A). As with any certification, check the lab’s own directory, not the box: our UL 3700 guide shows how.
• Plug appliances into it, not it into your house. UL 2743 doesn’t cover packs that are permanently connected to a home’s wiring, supply power to it or interact with the utility; those fall under UL 9540, the standard for energy storage systems. UL Solutions has warned that power packs certified only to UL 2743 and sold to be wired in as home battery storage aren’t certified to the right standard for that (UL Q&A). Connecting anything to your home’s wiring is a job for a licensed electrician.
• Medical devices: if someone at home depends on one, ask the device’s maker or your doctor what backup it needs, rather than sizing it from a table like this.

Bottom line

Size a portable power station for both numbers: output watts for what runs at once, with surge for anything with a motor, and watt-hours for how long, divided by about 0.85 for losses. For lights, phones, a laptop and a fan, around 1,000 to 1,200 Wh covers an evening; a fridge for a day takes it toward 2,700 Wh; air conditioning roughly doubles that again. Use your own appliances’ rating plates where you can, and check the station’s listing in the lab’s directory.

How we got these numbers

Appliance figures are the median of every model certified by ENERGY STAR in each group, downloaded from ENERGY STAR’s open data on November 5, 2026 by our sizer’s data script: on-mode or rated power for TVs, laptops, fans and lights, annual energy use ÷ 365 for fridges, and, for window air conditioners, cooling capacity divided by the efficiency rating (CEER), our estimate of the draw while cooling. The 85% usable share and 25% headroom are our own rough assumptions, not a standard. The scenarios and their hours are illustrations, not measurements of any home.