How long will my power station last? Backup power calculator
List what you want to keep on during a blackout and see how long a power station, a UPS or a battery lasts, which size to buy, whether it recharges between outages, how many solar panels you need and what a generator costs. Every formula is shown.
My appliances
Change any numberPower is what the appliance draws from the socket (the label or the manual; a plug-in meter tells it best). “Start ×” is how many times more a motor or a compressor draws for a moment when it starts. “Runs, %” is the share of the time it really draws power: a fridge compressor runs about a third of the time.
Total
How it is calculated
Battery
Inverter (the station’s sockets)
The rated and peak power are on the station’s label. Own consumption is what the inverter burns with nothing plugged in: 5–30 W for a station, more for a big UPS. If the peak power is unknown, leave it empty: twice the rated power is assumed.
Result
How it is calculated
The reverse calculation: for the appliances on tab 1 and the battery type on tab 2, how big a station or UPS battery must be to last the whole outage.
What you need
Station classes by capacity
Classes are rough and brand-free. Compare the usable capacity in Wh and the continuous power in W on the label, the inverter type (pure sine), the charging power and the battery chemistry. A UPS with an external battery for a gas boiler is sized the same way: its battery in Ah × V is in the table.
How it is calculated
Charging power
The charging power is on the label or in the manual (AC input, W). Many stations let you choose a slower, gentler charge: enter the one you use. A generator charges through the same socket input, at most at 80 % of the generator’s power (tab 6).
Outage schedule
How it is calculated
How it is calculated
Generator
Prices
How it is calculated
Self-test
Safety first
Read before the next outageAll numbers are estimates: real appliances, batteries and generators differ from their labels, and the formulas behind every result are shown under “How it is calculated”. When it matters (medical equipment, heating), plan with a margin and check with a plug-in power meter.