How to Size a Portable Power Station for Your Home
To size a portable power station, add up the running watts of everything you need to power at once, confirm the unit’s surge rating covers your biggest motor-driven load, then multiply your running watts by the hours you want to run to get the watt-hours (Wh) of battery capacity you need. Most households land between 500 Wh for keeping phones, a router, and a few lights alive and 2,000-3,000 Wh for riding out a multi-hour outage with a refrigerator and a medical device. The right size is the one that covers your real loads with about 20% headroom, not the biggest box on the shelf.
Start with what you actually need to run
Before looking at any spec sheet, write down the specific things you want powered during an outage and for how long. Be honest about need versus nice-to-have. A typical priority list looks like this:
Refrigerator, which keeps food safe (a closed fridge holds temperature for about 4 hours)
Phone and laptop charging to stay reachable and informed
Wi-Fi router and modem for internet and alerts
A few LED lights
Medical equipment such as a CPAP or oxygen concentrator
Sump pump, if you have a basement and flooding risk
What you leave off the list matters just as much. Electric ranges, central air conditioning, and electric water heaters draw far more than a portable station is built for; those belong on a whole-home or partial-home system.
Add up your running watts
Every device draws a steady, continuous load called running watts. Add the running watts of everything you would run at the same time. Useful real-world figures:
Refrigerator: about 100 to 200 W running
CPAP without humidifier: about 30 to 60 W
Wi-Fi router and modem: about 10 to 30 W
LED light: about 10 W each
Laptop: about 50 to 100 W
One-third hp sump pump: about 800 W running
A common kit (fridge, router, a couple of lights, and phone charging) adds up to roughly 250 to 400 running watts. That number is the minimum continuous output your power station must deliver.
Don’t forget surge watts
Anything with a motor or compressor briefly pulls surge watts when it kicks on, often two to four times its running watts. A fridge that runs at 150 W can spike to 1,200 to 1,800 W for a second or two. Your power station’s surge rating has to clear that peak, or the unit will trip even though its continuous rating looked fine. Always size to the single largest surge load on your list.
Convert to watt-hours for runtime
Output (watts) tells you what you can run; capacity (watt-hours, or Wh) tells you how long. The math is simple: running watts times hours of runtime equals the watt-hours you need. A refrigerator’s compressor cycles on and off, so it averages roughly one-third of its running wattage over an hour, meaning a 150 W fridge uses closer to 50 Wh per hour in practice. That is why a 2,000 Wh battery can keep a refrigerator cold for 10 to 20 hours, depending on efficiency and how often the door opens.
A worked example for a basic outage kit running about 250 W on average:
Over 4 hours: about 1,000 Wh
Over 8 hours: about 2,000 Wh
Over 12 hours: about 3,000 Wh
Add about 20% headroom for battery efficiency losses and cold-weather performance, and round up to the nearest available size.
Match the numbers to a tier
Once you have your two numbers, peak surge watts and total watt-hours, you can shop by tier instead of by brand:
Small (300 to 600 Wh): phones, laptop, router, and a couple of lights. Apartment and renter friendly.
Mid (1,000 to 2,000 Wh): adds a refrigerator and a CPAP through a short-to-medium outage. The most common household pick.
Large (2,000 to 3,500-plus Wh, often expandable): refrigerator, medical device, sump pump, and lighting across a longer outage.
Fortify is vendor-neutral, so we point you to the right tier and a well-reviewed unit within it, not the most expensive box. You can compare options on the Fortify Shop, and see how we match needs to gear on How It Works. For outage planning beyond the hardware, our storm-season power-prep checklist covers the rest of the kit.
Frequently asked questions
What size power station do I need to run a refrigerator?
Plan for a unit with a surge rating above about 1,500 to 1,800 W to handle compressor startup, and at least 1,000 to 2,000 Wh of capacity to run a typical fridge for roughly 10 to 20 hours. A mid-tier station usually covers a refrigerator plus a few small loads.
Can a portable power station run my whole house?
No. Portable stations are built for essential loads such as a fridge, electronics, medical devices, and lights. Central AC, electric ranges, and electric water heaters need a whole-home or partial-home system.
How many watt-hours do I need for a CPAP overnight?
A CPAP without a heated humidifier draws about 30 to 60 W, so eight hours is roughly 240 to 480 Wh. Turn the humidifier off or down on battery to stretch runtime, since heating elements can double the draw.
Is it better to buy a bigger power station than I need?
A little headroom (about 20%) is smart, but oversizing wastes money and adds weight you will rarely use. Size to your real priority loads plus surge, and pick an expandable model if you want room to grow.
Written by The Fortify Resilience Desk. Fortify is a vendor-neutral resilient-power company that helps households and property owners buy code-compliant, right-sized backup power. Sources: FEMA Ready.gov, the USDA Food Safety and Inspection Service, and manufacturer wattage charts.
