About the calculator
Who it is for
Texas households that have been through a long outage, such as Winter Storm Uri in February 2021 or the Houston-area storm outages after Hurricane Beryl in July 2024, and now want one answer: with my appliances, how many hours will each backup option last? The page does not tell you what to buy. It does the arithmetic on your own list.
What you put in
- Appliances: watts, hours per day and quantity for each row, plus an optional starting-watts figure for motors and compressors. Blank starting watts count as three times running watts.
- The outage: summer or winter, and any length from 1 to 720 hours.
- Usable share of battery capacity, from 50% to 100%. We assume 85% for conversion loss; change it to your unit's spec.
- An optional unit of your own: watt-hours, continuous watts and surge watts.
What comes out
For each built-in battery preset and any unit you add, the calculator gives hours of runtime, whether the load fits the unit's continuous and surge ratings, and a verdict for your chosen outage length. It also estimates propane or natural gas burn for a standby generator, and a printable outage plan for the fridge door. Solar recharging is not counted.
How we checked the numbers
Every default wattage, battery specification and safety rule has a named document, a link and the date we read it, listed on the sources and method page. Where we use our own assumption, such as 85% usable capacity or the 8-hours-in-24 duty cycle for a refrigerator, the page says so.
How we make money
Right now this site earns nothing and has no live affiliate links. We are applying to the Amazon Associates program. If it accepts us, some links to products on Amazon.com will be affiliate links: they will be labelled where they appear, carry rel="sponsored", and we may earn a commission when you buy, at no extra cost to you. The calculator math does not change based on who pays us, and we keep unfavorable results visible, such as a unit that is too small for your load.
Who runs it
Spicewood Secure Storage LLC, Spicewood, Texas. Corrections and questions: [email protected].
Limits you should know
We are not an electrician, utility, insurer or medical adviser. If a power failure puts a person's health at risk (oxygen, CPAP, refrigerated medicine), talk to the device supplier and your utility about priority and backup options, and have a plan that does not rely on this page.