Most shoppers looking for home backup power begin by asking the wrong question: which product should they buy? The critical question must come first — exactly how many hours of backup does your home require? This is not a matter of guesswork, as the U.S. Energy Information Administration provides the answer annually, with the 2024 figures making the calculations exceptionally clear.
The 2024 outage picture
The main takeaway is that U.S. electricity customers averaged 11 hours of power interruptions in 2024, according to the EIA’s Electric Power Annual 2024, which was summarized in a December 2025 analysis. This duration is nearly double the annual average recorded over the previous decade. Severe events, such as Hurricanes Beryl, Helene, and Milton, were responsible for roughly 80% of those outage hours. Major event-related interruptions averaged nearly nine hours per customer in 2024, contrasting sharply with the roughly four hours per year seen between 2014 and 2023. Meanwhile, routine outages unconnected to major events remained consistent at about two hours annually.
The industry relies on two specific metrics worth keeping in mind. SAIDI, or the System Average Interruption Duration Index, measures the cumulative outage time experienced by an average customer throughout the year. SAIFI, the System Average Interruption Frequency Index, tracks how often the power actually goes out. When sizing backup power, SAIDI is the vital metric because capacity depends on both duration and load rather than duration alone.
However, national averages can be misleading because they smooth over severely impacted areas. Hurricane Helene disrupted power for roughly 5.9 million customers across 10 states, while Beryl knocked out 2.6 million in Texas. In South Carolina, customers faced an average of 52.3 hours without electricity in 2024, a stark jump from the 2.0 to 5.4 hours recorded in each of the four preceding years. Furthermore, a separate five-year review of federal reliability data revealed that a typical U.S. state lost 4.9 hours annually between 2020 and 2024, whereas Louisiana averaged 33.5 hours. Residents in storm-prone regions should therefore disregard the national mean and focus instead on the major-event figure for their specific state. How long it takes to restore power after an outage in any given area depends on storm severity, utility crew access, and grid damage, which together establish your duration target.
From duration to capacity: the sizing equation
Only three variables determine the outcome. Required capacity in watt-hours equals planned outage hours multiplied by the combined wattage of all running appliances, multiplied again by a safety margin of 1.2 to 1.5 to account for inverter losses and personal estimation errors.
Working through the math makes it intuitive. A refrigerator consumes roughly 150 watts while running. Adding LED lighting, a Wi-Fi router, and phone charging adds about 100 watts combined, bringing the essential load to 250 watts. Based on the 2024 national average of 11 hours, this equals 2,750 watt-hours. Applying a 1.25 safety margin yields a target of roughly 3,400 watt-hours. For a household in a storm-prone zone extending that duration to 24 hours, the same 250-watt load requires 7,500 watt-hours before factoring in the margin.
What belongs in the load list
Your appliance inventory is the most crucial decision you will make. Begin by prioritizing items that protect health and property, such as refrigeration. Medical equipment like a CPAP machine utilizes about 40 watts, while a sump pump requires approximately 800 watts in areas susceptible to flooding. Next, incorporate communication and lighting necessities: a router (~10W), LED bulbs (~10W each), phone chargers (~10W each), and a laptop (~65W).
Unless your budget has substantial room, leave heavy heating appliances off the list. A single portable space heater operating at 1,500 watts consumes as much energy in one hour as a refrigerator uses in ten. Sizing for essentials first ensures that both capacity and cost remain grounded in actual outage data rather than worst-case comfort scenarios.
Why the average is the wrong target
Because SAIDI is an average, it can be heavily skewed by extreme events. With 80 percent of all outage hours stemming from major events in 2024, sizing your system solely for a routine two-hour blackout leaves you prepared for normal days but vulnerable the moment a hurricane stalls over your county. The EIA data points clearly toward sizing for your state’s major-event duration and adding a safety margin. Once your device list and duration target are finalized, a portable power station calculator performs the arithmetic to verify whether a given unit’s watt-hour rating truly supports your plan.
To summarize: take the regional EIA duration, multiply it by your measured essential load, include a safety margin, and purchase your system once. Outage trends continue to favor longer, storm-driven blackouts, meaning capacity planned against that trajectory is capacity that will perform when needed. Anchor table (for client verification)
