Sizing tool
How much capacity do you actually need?
Most buyers overspend by 40%. Pick what needs to stay on, set runtime per device, and we'll match a unit. Recommendations link to live Amazon listings.
Sizing calculator · Livev2.4
What needs to stay on?
Select essentials and adjust runtime per device. We add a 20% safety buffer.
Essentials
Refrigerator
150W
8h
CPAP machine
60W
Medical device
80W
LED lights (×5)
50W
5h
Phone charging
18W
4h
Wi-Fi router
15W
24h
Comfort
Laptop
65W
50" TV
100W
Box fan
75W
Space heater
1500W
Sump pump
800W
Kitchen
Microwave
1000W
Coffee maker
800W
Electric kettle
1500W
Induction burner
1500W
How it works
We multiply each device's watts by the hours you need it, sum the totals, then add 20% as a buffer for inverter losses and cold-weather de-rating.
What we don't model
Surge loads (motors, compressors), solar input, or cycle-to-cycle battery wear. The buffer covers the first; for solar and longevity, see our buying guides.
Want a deeper read?
Our LFP vs NMC guide explains why cycle life matters more than peak Wh for most home backup buyers.