Pick the appliances you want to keep running during a power outage. The calculator shows how much energy they use per day, how much power they draw at once, and how long a portable power station or home solar battery will last. You can edit the watts and hours to match your own devices.
Backup Battery Runtime Calculator
1. Choose appliances (edit watts and hours per day)
| Use | Appliance | Watts | Hours/day |
|---|
Estimates only. Watts are typical running values; check the label or measure with a plug-in energy meter. Motors and compressors (fridges, freezers, pumps, AC) can draw 2–3× their running watts for a moment when they start, so choose an inverter with enough surge rating. Solar recharging is not included.
Calculator by HotGadgetsInfo
How the calculator works
- Daily energy (kWh) = watts × hours per day ÷ 1,000, added up for every appliance you select. A fridge averaging 150 W for 10 compressor hours uses about 1.5 kWh a day.
- Runtime = usable battery capacity ÷ daily energy. Usable capacity is lower than the rated capacity because of inverter losses and battery reserve. 85% is a realistic default for most power stations and home batteries.
- Inverter output = total watts of everything running at once. Capacity (kWh) decides how long the battery lasts. Output (W) decides what it can power at the same time. You need enough of both.
- Surge: appliances marked ⚡ have motors or compressors that briefly pull 2–3 times their running watts when they start. Your inverter’s surge rating needs to cover this.
Typical appliance wattage for home backup
| Appliance | Running watts | Startup surge | Typical daily use |
|---|---|---|---|
| Refrigerator | 100–200 W | 600–1,200 W | 1–2 kWh |
| Chest freezer | 60–100 W | 300–600 W | 0.5–1 kWh |
| Wi-Fi router + modem | 15–25 W | — | 0.4–0.6 kWh |
| LED bulb | 8–12 W each | — | 0.05 kWh per bulb |
| Laptop | 45–90 W | — | 0.3–0.6 kWh |
| CPAP machine | 30–60 W | — | 0.3–0.5 kWh |
| Sump pump (1/3 hp) | 800 W | 1,500–2,500 W | Varies with rain |
| Gas furnace blower | 400–800 W | 1,000–1,500 W | 2–4 kWh in winter |
| Window AC | 500–1,400 W | 1,500–2,500 W | 3–8 kWh |
| Microwave | 1,000–1,500 W | — | 0.2–0.4 kWh |
Related guides
- How to Measure Appliance Energy Use Before Buying a Home Backup Battery
- What Size Portable Power Station Do I Need?
- Best Portable Power Stations for Home Backup
- What Can a 10 kWh Solar Battery Run?
- How Many Solar Batteries Do I Need?
- Solar Battery Backup for a Refrigerator
- Best Solar Battery Backup System for Home
- Best Home Energy Monitors
Use this calculator on your site
Preppers, solar installers and emergency-preparedness sites are welcome to link to this calculator or use the wattage chart with credit and a link to hotgadgetsinfo.com/backup-battery-runtime-calculator.