Portable Power Station Sizing: Add Up Watts First

Most people buy a portable power station the way they buy a suitcase: grab the medium one and hope. Then the fridge kicks on, the unit beeps, and the whole thing shuts off with the display still showing plenty of charge left. Nothing was broken. The math just never got done. Portable power station sizing comes down to two separate numbers, and mixing them up is the single most common reason a perfectly good unit disappoints its owner.

Here is the short version. Watts (W) describe how much power your devices pull at the same moment — that decides whether the unit can run them at all. Watt-hours (Wh) describe how much energy is stored — that decides how long it runs. You need to clear both bars. A big battery with a small inverter will refuse to start your microwave; a strong inverter on a small battery will run it for four minutes. Add up your appliances, note their surge draw, and both numbers fall out of the list almost automatically.

What do watts, watt-hours and surge watts actually mean?

Three terms do all the work here, so it's worth nailing them down before you look at a single product page.

• Running watts — what a device draws while it's humming along normally. A laptop charger might be 60 W, a box fan 50 W, a full-size refrigerator 120–200 W while the compressor is running.
• Surge (or starting) watts — the brief spike when anything with a motor or compressor kicks on. Fridges, sump pumps, power tools and air conditioners can pull two to four times their running watts for a second or two. A 150 W fridge can momentarily demand 600 W or more.
• Watt-hours — running watts multiplied by hours. A 60 W laptop setup for 5 hours is 300 Wh. This is the number printed on the side of the battery, and it's the one that tells you how long the party lasts.

Product listings quote an output rating (continuous watts, sometimes with a separate surge figure) and a capacity in watt-hours. Those two specs map exactly onto the two questions above. Everything else — port count, charge speed, weight — matters, but only after these two clear.

Where to find the wattage of your own stuff

You don't have to guess. Nearly every appliance has a label on the back, the bottom, or the power brick listing watts, or listing volts and amps. If you only see volts and amps, multiply them: 120 V × 1.5 A = 180 W. Laptop and phone chargers print their output right on the brick. For anything stubborn — an older fridge, a well pump — a plug-in energy meter from a hardware store will show you real draw over a full cycle, which is far more honest than the nameplate.

How do I add up the watts I actually need?

Build a list. Not a mental list — an actual written one, because the whole point is to catch the appliance you forgot. Four columns: device, running watts, surge watts, hours you'd realistically use it.

A power-outage list for a small household might look like this:

• Refrigerator — 150 W running, roughly 600 W surge, cycling about 8 hours over a day
• Two phone chargers — 20 W each, 3 hours
• Laptop — 60 W, 5 hours
• Wi-Fi router and modem — 20 W, 24 hours
• LED lamps ×3 — 30 W total, 6 hours
• CPAP or small medical-free electronics, box fan — 50 W, 8 hours

Now do two separate sums.

Sum one: simultaneous watts. Add the running watts of everything that will genuinely be on at the same moment. In the list above that's roughly 150 + 40 + 60 + 20 + 30 + 50 = 350 W. Then find the single largest surge in the group and make sure the unit can absorb it on top of the baseline. The fridge spiking to 600 W while 200 W of other things are running means you want an inverter comfortable with roughly 800 W in that instant. This is why listings quote both a continuous rating and a higher surge rating — check the surge number, not just the headline one.

Sum two: watt-hours. Multiply each device's running watts by its hours, then add. The fridge is the trick here: compressors cycle, so a fridge doesn't draw 150 W for 24 straight hours. A common planning approach is to assume it runs about a third of the time — call it 8 hours of actual compressor time, so 1,200 Wh. Add the rest: chargers 120 Wh, laptop 300 Wh, router 480 Wh, lights 180 Wh, fan 400 Wh. Total: about 2,680 Wh for a full day.

Then add headroom — two kinds

Your raw total is a floor, not an answer. Two adjustments:

1. Efficiency loss. Converting stored DC power to household AC isn't free. Plan on using somewhere around 85% of the labeled watt-hours in real AC output. Divide your total by 0.85 — that 2,680 Wh becomes roughly 3,150 Wh of rated capacity.
2. Life happens. The outage lasts longer than forecast, or someone plugs in a kettle. A 20–25% cushion above your calculated need is the difference between a tool and a source of anxiety. Don't buy triple, though — capacity is weight and money you carry around forever.

Run the same arithmetic for a camping weekend and the answer looks completely different: no fridge means the watt-hour number collapses, while a portable induction burner would blow past the output rating of a small unit. Size for the scenario you'll actually face most often, and note the second-most-likely one so you know what you're giving up.

What capacity class fits my situation?

Once your two numbers exist, they land you in a rough class. Treat these as orientation, not gospel — your list beats any chart.

• Roughly 200–500 Wh, output under about 500 W. Phones, tablets, laptops, cameras, a CPAP-sized draw, string lights. Carry-in-one-hand territory for camping, tailgating and travel. Won't start a fridge.
• Roughly 500–1,000 Wh, output around 1,000 W. The versatile middle. Runs a mini fridge, a TV, fans, a coffee maker in short bursts. Good for car camping and short outages.
• Roughly 1,000–2,000 Wh, output 1,500–2,200 W. Full-size fridge plus electronics through a day-long outage, most kitchen small appliances, corded tools. Heavy enough that wheels and a handle start to matter.
• 2,000 Wh and up, often expandable. Multi-day backup, well pumps, window AC units, RV use. This is where expansion battery compatibility earns its keep — buy the base now, add capacity later rather than guessing high on day one.

Specs worth checking after capacity

With the two big numbers settled, scan the listing for these:

• Battery chemistry. LiFePO4 (lithium iron phosphate) cells are rated for far more charge cycles than older lithium-ion, and manufacturers publish the cycle count and the percentage of capacity retained at that point. Look for both figures together — "3,000 cycles to 80%" tells you much more than "3,000 cycles."
• Pure sine wave output. Standard on most current units, but confirm it if you're running anything with sensitive electronics or a motor.
• Recharge inputs. AC wall time, maximum solar input in watts, and whether it charges from a car outlet. If solar is part of your plan, the panel wattage you can feed it caps how fast you refill.
• Pass-through charging — can it power devices while it's charging? Useful during rolling outages.
• Port lineup. Count the AC outlets, USB-C wattage (a 100 W PD port replaces a laptop brick), and any 12 V outputs.
• Weight and handles. A 2,000 Wh unit is a genuinely heavy object. Check the pounds before it arrives, not after.

Where should I shop once I know my number?

The useful thing about doing the math first is that it turns shopping from browsing into filtering. You walk in knowing "at least 1,500 Wh, at least 1,800 W continuous, LiFePO4, needs to take 400 W of solar" — and most of the catalog eliminates itself in thirty seconds.

For that kind of side-by-side comparison, the portable power station and solar generator lineup at Jackery CA is an easy place to run your list against real spec sheets, since capacity, continuous output, surge rating and solar input are all listed per model and the range spans small carry-along units through expandable home-backup sizes. Pull up two or three candidates that clear both of your numbers, then let the secondary specs — weight, recharge time, port mix — break the tie.

One field note from watching how people shop this category: the regret usually runs in one direction. Buyers who sized carefully and went one class up rarely mention it again; buyers who rounded down talk about it every outage. If your list puts you right on the boundary between two sizes, the larger one is usually the calmer choice — as long as you can still lift it.

Common questions

How many watt-hours do I need to run a refrigerator?

A full-size refrigerator draws roughly 100–200 W while the compressor runs, and compressors typically cycle about a third of the time. That works out to somewhere near 1,000–1,500 Wh per day for the fridge alone, before efficiency losses. Check your own model's label, and make sure the unit's surge rating can absorb the compressor's startup spike.

What is the difference between running watts and surge watts?

Running watts are the steady draw while a device operates normally. Surge watts are the brief spike when a motor or compressor starts, often two to four times higher and lasting only a second or two. A power station has to clear both: its continuous output rating covers running watts, and its separate surge rating covers that startup moment.

Can a portable power station run a space heater or air conditioner?

Space heaters commonly draw 1,500 W continuously, which exceeds many units' output rating and drains even a large battery in about an hour. Small window air conditioners are more feasible on a high-output unit, but plan on 500–1,200 W of continuous draw plus a startup surge. Check both the appliance nameplate and the unit's continuous rating before assuming it fits.