Select your devices
Each device shows its watts and a typical daily run time you can adjust. Use the + button to add more than one, and edit the hours to match your real usage.
Your estimate
Select devices to get started
Use the + buttons above to add everything you want to power.
How is the battery size calculated?
Daily energy (Wh) is what you actually use, in watt-hours: each device's watts multiplied by how many hours a day you run it. Your generator's battery must hold at least this much.
Battery needed adds a safety reserve. We size the battery for 1.5× your daily Wh (roughly a day of headroom) and treat about 20% of rated capacity as unusable, LiFePO4 batteries shouldn't be drained to zero, and output efficiency isn't perfect.
Solar panel is sized to recharge a full day's use in a typical day of sun. We assume about 4.5 hours of useful sunlight and that panels deliver ~80% of their rating in real conditions.
More tools and guides
Explore the rest of the backup-power toolkit:
- Generator size calculator (gas generator sizing)
- Fuel & runtime estimator (how long will it run on a tank?)
- Generator wattage chart (running & starting watts)
- Portable vs standby generator (which should you buy?)
- What size generator for a well pump? (1/2 HP and 1 HP, plus the 240 volt catch)
- What size generator for a sump pump? (1/2 HP and 1 HP, and why storms are worst)
- What size generator for a refrigerator and freezer? (startup watts plus food safety time)
- What will a 7,500 watt generator run? (a full worked example)
How many watts do common devices draw?
| Device | Running watts | Rough daily use |
|---|---|---|
| Refrigerator (full-size, cycling avg) | ~60W avg | 1.2–1.6 kWh/day |
| Chest freezer (cycling avg) | ~35W avg | 0.7–1.0 kWh/day |
| CPAP machine | ~60W | ~8 hrs/night |
| Laptop computer | ~70W | 2–4 hrs |
| LED lights (whole room) | ~40W | 4–6 hrs |
| WiFi router + modem | ~20W | 24 hrs |
| Smart TV (50″) | ~110W | 3–4 hrs |
| Phone / tablet charging | ~15W | all day |
Fridge and freezer wattage shown is the running average to account for compressor cycling on and off all day. Actual draw varies by make, model, and age. Use the wattage printed on each device's label for accuracy.
Disclaimer: This is an estimate for planning purposes only. Actual battery capacity, output, and solar recharge vary by brand, weather, altitude, and device efficiency. Always check a power station's rated watt-hours and AC output watts against your needs, and consult the manufacturer's specs before buying. Never leave a lithium power station unattended while charging.