So you’re sold on getting a portable power station for backup; but how big does it need to be? It’s an important question, because these power stations come in all sizes from small 300Wh units up to gigantic 4000Wh monsters, and you don’t want to overspend or undersize. Calculating the right size basically comes down to figuring out what devices you want to run and for how long, then matching a power station to those needs. Don’t worry, we’ll break it down step by step in simple terms. Grab a pen, list your essential devices (we’ll use a fridge as a key example), and let’s do a little math to guide our decision.
- List Your Essential Devices and Their Wattage: First, make a short list of what you absolutely need to power during an outage. Common essentials are refrigerator, maybe a freezer, some lights (LED lamps), phone chargers, a Wi-Fi router, possibly a fan or small heater, and any critical medical devices like a CPAP machine. Now, find out how many watts each device uses. You can usually find a label or the manual that says something like “Power: 60W” or “120V ~ 1.2A” (if you have amps, multiply by 120 to get watts, so 1.2A = 144W). Here are some typical numbers:
- Refrigerator (full-size): 150-300W running, but 800-1200W surge when compressor starts. (Modern Energy Star fridges might only use ~120W average.)
- Freezer (chest): ~150W running, similar surge ~300-600W.
- CPAP machine: 30-60W while running (without heated humidifier).
- Wi-Fi Router/Modem: ~10-15W.
- LED light bulb: 5-10W.
- Laptop computer: 50-100W (charging).
- Phone charger: 5-10W.
- Fan (box fan): 50-100W on high.
- Space Heater: 1000-1500W (very high, try to avoid on battery).
- Sump Pump (1/2 HP): ~1050W running, 2000+ W start (important surge consideration).
- Microwave: 800-1200W while running.
Jot down the wattage for each thing you’d like to run simultaneously. Suppose we decide during an outage we want to run: a refrigerator (let’s say 200W average draw), 1 LED lamp (10W), 2 phone chargers (say 10W each = 20W), a Wi-Fi router (10W), and occasionally a laptop (60W) or a fan (50W). If all that ran at once, the total continuous wattage would be about 200 + 10 + 20 + 10 + 60 = 300W (I didn’t include the fan yet, assuming laptop OR fan, not both). Now, check the peak/surge: the fridge might spike to 1000W for a few seconds when compressor kicks in. So we need a power station that can handle ~1000W surge and ~300W continuous comfortably. Most mid-size units (around 500-1000Wh capacity) have inverters rated 500W to 1000W, which would cover this scenario. If you had a well pump or wanted to run a microwave, you’d need a higher output rating, maybe 1500-2000W.
- Determine How Long You Need to Run Them (Watt-hours): Power station sizes are usually given in watt-hours (Wh), which is basically how many watts it can supply for one hour. For example, 500Wh means 500 watts for 1 hour, or 250 watts for 2 hours, and so on (in practice there are some efficiency losses, but we’ll approximate). Let’s continue our scenario: say you want to get through a 24-hour outage comfortably. Does that mean running everything non-stop 24h? Not really; your fridge’s compressor actually cycles (maybe runs 50% of the time or less if kept closed), lights you’ll only have on at night, etc. But to keep it simple, let’s estimate consumption over 24h:
- Fridge: If 200W when running, but it runs maybe 12 hours total in a day (on and off cycling), that’s 200W * 12h = 2400 Wh.
- Wi-Fi + chargers + small stuff: roughly 50W combined, if run 24h that’s 50W * 24h = 1200 Wh (though at night you might not need Wi-Fi or lights, so this is probably high).
- Laptop a few hours, fan a few hours; maybe another 500 Wh.
Add them: ~2400 + 1200 + 500 = ~4100 Wh for a full day. That suggests a very large power station (over 4 kWh) would be needed for 24 hours continuous. But you can significantly cut that down with energy-saving strategies: limit fridge opening so it runs less, maybe turn off the fridge for a couple hours at a time (it will hold temperature if unopened), turn off Wi-Fi at night, etc. It’s quite feasible to cut usage in half. Many people find that around 1000-1500Wh can get them through a daytime or nighttime period with careful use, especially if not running a fridge continuously.
Another approach is to think in terms of daily recharge: If you have a smaller power station, you could run the essentials for, say, 8-12 hours, then plan to recharge it (via solar or a generator or your car) during the day for the next stretch. For instance, a 1000Wh unit might run a fridge (cycling) and a few lights/chargers for roughly 8-12 hours. With some solar input in the morning, you could extend that further.
- Match to a Power Station Size: Once you have an estimate of your daily watt-hour needs and the peak watts needed, you can choose a power station. If our target is about 2000Wh per day and 500W peak, a station around 2000Wh (aka 2 kWh) would get you through ~24 hours without recharge. If you only need ~500Wh per day (maybe just a CPAP and phone chargers for overnight), a smaller ~500Wh unit could suffice. It’s usually wise to oversize a bit because you rarely want to fully drain a battery to 0%. Many manufacturers actually recommend not going under 10-20% for longevity. Also, advertised capacity (like “1000Wh”) is the battery size, but the usable output might be 85-90% of that due to inverter efficiency. So factor in a little overhead.
Let’s consider a common scenario: Keeping a fridge running through an overnight outage. What size do we need? A fridge might use ~120W average over the night (accounting it cycles on/off). For, say, 10 hours of night: 120W * 10h = 1200 Wh. So a station of at least 1200Wh is recommended to be safe. Something like a Jackery Explorer 1500 (1488Wh) or EcoFlow Delta (1260Wh) could handle that. If you only wanted to keep food cold and a light on, you might scrape by with 500-600Wh by running the fridge sparingly (e.g., power it 1 hour on, 2 hours off; many modern fridges are well insulated enough for that pattern). But if you want more peace of mind or a longer duration, go 1000Wh+.
For a CPAP user: Let’s do that as another example because it’s common. A CPAP draws ~40W on average. For 8 hours sleep, that’s 40W * 8h = 320 Wh. If you have a 500Wh power station, it could run the CPAP for one night easily with ~35% to spare. If you also want some fan or laptop usage, you’d want maybe 700-1000Wh for an overnight camping trip or outage. So a 500Wh unit is minimum for one night of CPAP, and something around 1000Wh if you want two nights or extra devices. (Note: using CPAP without the humidifier saves a ton of power, as humidifiers can double the wattage.)
Using manufacturer guides: Some companies give usage charts. For instance, EcoFlow suggests: Lights + phone charging only might need a 500-1000Wh station; running a fridge, Wi-Fi, lights might need 1000-3000Wh; whole basic household for a day might be 3000-5000Wh+. This aligns with our calculations that bigger homes or longer outages push into multiple kilowatt-hours.
Don’t forget the inverter rating: If your total wattage (at a given moment) exceeds the inverter’s output, the power station will overload and shut off. So ensure the station’s Watt output exceeds your highest combined load. If you want to occasionally run a microwave (1000W) or coffee maker (800W), you’ll need a station with at least ~1000W output. If you only plan on lights and a fan, a 300W output station is fine. Always check both the Watt-hour (Wh) capacity and the Watt (W) output rating when sizing.
Final thoughts on sizing: It’s often better to err on the larger side if budget allows, because you can simply run more devices or go longer between recharges. However, larger units are heavier and pricier. For basic emergency backup (fridge, phones, light), many households find a 1000-1500Wh (1 to 1.5 kWh) unit with ~1000W output hits a sweet spot of portability and usefulness. If you have critical needs (well pump, multiple days off-grid), then investing in a 2000+ Wh system makes sense. If you’re just keeping a few electronics up for short outages, a 500Wh can do the job affordably.
Do a personal audit: add up the watts you’ll use at once to size the inverter, and add up the watt-hours you’ll consume to size the battery. And remember you can prioritize; maybe you won’t run everything all at the same time or all night. With this info, you can confidently choose a power station that’s not too small (leaving you powerless too soon) and not overkill for your budget. It’s all about balance!