What Size Portable Power Station Do I Need?
Buy too small and your fridge dies at 2 a.m. Buy too big and you paid $2,000 to haul 60 pounds of battery you never use. Sizing a portable power station is simple once you know the two numbers that matter and one easy formula. This guide walks you through both, with real device numbers and worked examples.
- Wh vs W: the two numbers that matter
- The sizing formula
- Device wattage reference table
- Scenario walkthroughs
- Surge wattage: the startup spike
- How to read a spec sheet
- Pick your tier
- Common sizing mistakes
Wh vs W: the two numbers that matter
Every power station is described by two numbers, and confusing them is the most common sizing error.
Watt-hours (Wh) is capacity: how much total energy the battery holds. Think of it as the size of the fuel tank. A 1,000Wh station holds twice the energy of a 500Wh station, so it runs your gear roughly twice as long.
Watts (W) is output: how much power the station can deliver at one moment. Think of it as the size of the engine. A station rated for 1,800W can run devices whose combined draw stays under 1,800W. Plug in a 2,000W load and it shuts off to protect itself, no matter how many watt-hours are in the tank.
You need both numbers to be big enough. Capacity determines how long things run. Output determines what can run at all.
The sizing formula
Here is the whole method in one line:
Required Wh = (total device watts x hours of use) / 0.85
The 0.85 accounts for inverter loss. Converting the battery’s DC power to household AC wastes roughly 10 to 15 percent as heat, so you only get about 85 percent of the rated capacity as usable AC power. Sellers rarely mention this. Size without it and you come up short.
Steps:
- List every device you want to run during an outage or trip.
- Find each device’s running watts (check the label, the manual, or the table below).
- Multiply watts by the hours you will run it. Add everything up.
- Divide by 0.85.
- Pick a station with at least that much Wh and enough W output to cover your highest simultaneous load.
Device wattage reference table
Typical running watts for common devices. Real numbers vary by model, so check your own labels when it counts. Fridges and anything with a motor cycle on and off, so their average draw is lower than the running watts shown.
| Device | Typical running watts | Notes |
|---|---|---|
| Smartphone (charging) | 5-10W | One full charge is about 10-15Wh total |
| Tablet | 10-18W | |
| Laptop | 45-90W | Gaming laptops can exceed 150W |
| LED light bulb / lamp | 5-15W | |
| WiFi router | 5-15W | Runs 24/7 in an outage; adds up |
| Box fan | 50-75W | |
| LED TV (32-43 in) | 40-80W | |
| 12V compressor fridge (camping) | 35-60W average | Cycles on and off; daily use roughly 300-700Wh |
| Full-size refrigerator | 100-200W running | Cycles; roughly 1-2 kWh per day. Startup surge 600-1,200W |
| CPAP, no humidifier | 15-40W | One 8-hour night is roughly 120-320Wh |
| CPAP, heated humidifier on | 60-100W | One 8-hour night is roughly 480-800Wh |
| Microwave | 900-1,200W | No surge spike, but huge continuous draw |
| Electric kettle | 1,200-1,500W | Short bursts, but needs high output |
| Sump pump (1/3 HP) | 800W running | Startup surge 1,300-2,000W. See surge section below |
| Power drill (charging) | 50-100W | Charger draw, not drilling draw |
Scenario walkthroughs
Weekend camping: phones, lights, laptop
Two phones charging 2 hours (10W x 2h x 2 = 40Wh), LED string lights 5 hours (10W x 5h = 50Wh), laptop 2 hours (60W x 2h = 120Wh). Total: 210Wh. Divide by 0.85: about 247Wh. A 300Wh station covers this with margin. Add a 12V compressor fridge (about 500Wh per day) and you want 1,000Wh or more for a full weekend.
Home outage overnight: fridge, router, phones, lamp
Fridge running watts 150W, but it cycles roughly one-third of the time overnight: 150W x 8h x 0.33 = about 400Wh. Router 10W x 8h = 80Wh. Two phones = 40Wh. LED lamp 10W x 5h = 50Wh. Total: 570Wh. Divide by 0.85: about 670Wh. A 1,000Wh station handles this comfortably and leaves headroom. Also check output: the fridge’s startup surge (600W+) means you want at least 1,000W of continuous AC output.
CPAP for one night
No humidifier at 30W average: 30W x 8h = 240Wh, divided by 0.85 = about 282Wh. A 300-500Wh station is enough. With heated humidifier at 80W: 80W x 8h = 640Wh, divided by 0.85 = about 753Wh. Now you are in 1,000Wh territory. (There is a trick that stretches this further: a 12V DC adapter for your CPAP skips the inverter entirely. See our CPAP guide.)
RV weekend
12V fridge (500Wh/day), lights (50Wh), laptop (120Wh), fan (150Wh), phones (40Wh): roughly 860Wh per day, or about 1,700Wh for two days. Divide by 0.85: 2,000Wh. This is where 2kWh-class stations, or a 1kWh station plus solar panels recharging during the day, earn their keep.
Surge wattage: the startup spike
Anything with a motor or compressor draws a brief spike when it starts, often two to three times its running watts. A fridge that runs at 150W can pull 600 to 1,200W for a split second when the compressor kicks on. A sump pump running at 800W can surge past 1,500W.
Two rules:
- The station’s continuous output (W) must exceed your highest simultaneous running watts.
- The station’s surge rating must cover the biggest startup spike. Most stations surge to roughly double their continuous rating.
This is the number one reason small stations “can’t run a fridge” even though the math says they should. The capacity was fine; the inverter tripped on the compressor’s startup surge. If a fridge or pump is in your plan, do not buy below 1,000W of continuous output, and 1,500W+ is safer.
Pick your tier
| Capacity | Good for | Not enough for |
|---|---|---|
| 300-500Wh | Phones, tablets, lights, laptop top-ups, one CPAP night (no humidifier), desk backup during short outages | Fridges, multi-day trips, anything with a motor |
| 500-1,000Wh | Weekend camping with a 12V fridge, CPAP for 2 nights, keeping a full-size fridge cold for several hours | Overnight whole-home essentials, sump pumps, microwaves |
| 1,000-2,000Wh | Overnight home outage (fridge + router + lights + phones), RV weekends, CPAP for several nights | Well pumps, central AC, multi-day outages without solar |
| 2,000Wh+ | Extended outages, sump and well pumps, running a microwave or power tools, serious off-grid use | Whole-house backup for days (that is home battery territory) |
When in doubt between two sizes, go bigger if the weight and price are acceptable. Running a station at 30-50 percent depth of discharge instead of draining it daily also extends battery life noticeably.
How to read a power station spec sheet
Manufacturers bury the important numbers among marketing terms. Here is what to look for and what to ignore.
Capacity in Wh: the headline number. Sometimes listed as “1,024Wh” and sometimes as battery cell specs like “51.2V 20Ah” (multiply volts by amp-hours to get Wh). If a listing only gives “watts” for capacity, it is hiding something.
AC output in W (continuous): what the inverter sustains. Check that this is the continuous rating, not the surge rating, which is always bigger and always printed larger.
Surge in W: the brief peak, usually about double the continuous rating. Matters for fridges and pumps.
Battery chemistry: LiFePO4 (LFP) lasts 3,000-4,000 cycles and is the current standard. Older NMC lithium lasts roughly 500-800 cycles. For a backup device you may own a decade, LFP is worth prioritizing.
Recharge speed: listed as AC input watts or “0-80% in X minutes.” A 1,000Wh station with 1,200W AC input refills far faster than one with 300W input. For outage use, fast recharge is almost as important as capacity.
Solar input: given as max watts and a voltage range. Both matter. A 400W max with a 12-60V range behaves very differently from 400W with a 30-120V range when you are choosing panels.
Ignore: “peak power” claims without a continuous rating next to them, “up to X devices” without naming the devices, and any runtime claim that does not state the load in watts.
Common sizing mistakes
Buying on watts alone. A 2,000W station with 500Wh runs a microwave brilliantly for about fifteen minutes. Output without capacity is a party trick.
Forgetting inverter loss. That 1,000Wh rating is DC capacity. Usable AC is closer to 850Wh. The divide-by-0.85 step exists for a reason.
Ignoring surge. Covered above, but it bears repeating: compressors and pumps kill undersized inverters, not undersized batteries.
Not planning recharge. A station is a bucket, not a well. For multi-day outages, pair it with solar panels or plan wall recharges between uses. Check the station’s solar input watts before buying panels: a 200W max solar input means a 400W panel array is wasted money.
Oversizing. A 3.6kWh station weighs over 100 pounds and costs as much as a used car. If your actual need is 700Wh, the extra capacity buys you nothing but a hernia. Size for your real loads, then add 20-30 percent margin.
Run the formula with your own devices, check both the Wh and the W, respect the surge, and you will buy the right size the first time.
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Frequently asked questions
How many watt-hours do I need to run a full-size refrigerator?
A typical full-size fridge uses roughly 1 to 2 kWh per day because the compressor cycles on and off. For overnight backup (8 hours), a 1,000Wh station is the practical minimum, and you need at least 1,000W of continuous AC output to survive the compressor’s startup surge.
Is a 1,000W power station enough for home backup?
For overnight essentials, yes: a 1,000Wh station with 1,000W+ output keeps a fridge cold, the Wi-Fi router on, phones charged, and a lamp lit for about 8 hours. It will not run a microwave, well pump, or central AC.
What does dividing by 0.85 do in the sizing formula?
It accounts for inverter loss. Converting the battery’s DC power to household AC wastes roughly 10 to 15 percent as heat, so only about 85 percent of the rated watt-hours are usable. Skipping this step is the most common reason people buy too small.
Can a portable power station run a microwave?
Briefly, if the output is high enough: a 1,000W microwave needs a station rated for at least 1,000W continuous, ideally 1,500W+. But microwaves drain batteries fast — five minutes at 1,000W eats about 100Wh including inverter loss. It is an emergency option, not a meal plan.
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