Tool
Load List Builder
Most people shop by capacity and never work out what they wanted to run. This does it the other way around: choose the loads first, get the watt-hours, and see which stage that answer belongs to. Some selections come back marked as things not to put on a battery at all.
Build the list
What you actually want running in the first day
No medical or life-sustaining equipment appears in this list. That planning belongs with the equipment supplier and with your electric utility, including asking about a medical registry and priority restoration, and it is not something a calculator should be doing.
Sump Pump is also missing, for a different reason: this site publishes no hour figure for that load, so there is no honest watt-hours-per-day number to add here either. Sump Pump explains what to do instead.
People in the household
Is your heating electric
Your list, in the order it matters
| Load | Average draw | Hours in 24 | Wh over 12 h | Wh over 24 h |
|---|---|---|---|---|
| Phone Charging | 24 W | 3 | 36 Wh | 72 Wh |
| LED Lighting | 30 W | 6 | 90 Wh | 180 Wh |
| Refrigerator | 52.5 W | 24 | 630 Wh | 1,260 Wh |
Total over 12 hours
756 Wh
Total over 24 hours
1,512 Wh
The stage this list belongs to
The heaviest load you selected first becomes realistic at stage 3. Read that stage before buying anything, including the part about what it does not cover.
The formula on screen
- watt-hours over 24 hours = average watts x hours running in 24
- watt-hours over 12 hours = that figure halved
- Average watts come from the device pages, with the compressor duty share already applied where one exists. Phone charging is the only entry that scales with household size.
- These totals describe energy consumed, not the capacity to buy. A battery has to be larger than the total because of conversion loss, and it has to have enough stated output to start whatever motors are on the list.
Every figure this tool produces is an estimate, not a guarantee. It does not account for startup surge, temperature, battery age, or the efficiency of any specific model, and it says nothing about whether a given unit will start a given appliance.
What to do with the total
- The totals describe energy consumed, not the capacity to buy. A battery has to be larger than the total, because conversion loss and unusable capacity take a share before anything reaches an outlet.
- Capacity is only half the question. If anything on the list has a motor, the unit also needs enough stated output to start it, and that is a separate specification.
- Cutting the list is usually cheaper than buying more capacity. Switching the router off overnight and skipping the second fridge does more for a long outage than most upgrades.
- This is an estimate, not a guarantee, and it is built on assumptions about hours and duty cycles that are printed on the page so you can replace them with your own.