Home Backup Power Calculator
Select essential household loads to estimate output rating and battery capacity.
Select essential household loads to estimate output rating and battery capacity.
Select essential household loads to estimate output rating and battery capacity.
Enter your own equipment values. The calculator uses transparent assumptions so you can adjust efficiency, reserve and operating conditions.
Use Real Equipment Ratings
Select essential household loads to estimate output rating and battery capacity.
Calculator Guidance
Use the result for planning, then verify the exact product manual, nameplate ratings and operating limits.
Home Backup Power Calculator
Formula
Output rating covers simultaneous running watts plus the largest startup surge. Battery energy covers average load multiplied by hours and losses.
Typical Backup Tiers
| Tier | Running Load | Battery Range | Use |
|---|---|---|---|
| Basic | 300–800W | 1–3kWh | Lights, internet, fridge |
| Essential | 1–3kW | 3–10kWh | Furnace, refrigeration, electronics |
| Major | 3–8kW | 10–30kWh | Pumps and broad circuits |
Planning Limits
Loads Cycle
The calculator uses full running watts.
240V Loads
Need compatible output.
Central HVAC
Requires measured startup.
Fuel vs Battery
Generators and batteries size differently.
Transfer Equipment
Panel connections need approved hardware.
Critical Medical Loads
Require professional planning.
How to Use the Result in the Real World
Treat the calculated result as a planning baseline rather than an exact promise. Real systems lose energy through conversion, wiring, temperature effects and internal electronics, while appliances can draw differently from their nameplate ratings.
Leave practical headroom instead of selecting equipment that exactly matches the result. Extra margin helps with startup surges, battery aging, changing weather and future loads, and it reduces the chance that normal variation pushes the system beyond its limits.
When the result affects a major purchase, verify the important inputs. Measure appliance consumption when possible, check the exact inverter or charge-controller limits, and compare the calculation with the equipment manufacturer's specifications.
Frequently Asked Questions
Does this include cycling?
It conservatively uses full selected running watts.
How is surge handled?
It adds the largest selected startup surge.
Can it size central AC?
Not reliably without measured data.
What about 240V loads?
The backup source must support 240V.
Is a generator sized the same way?
Output is similar, but fuel replaces battery Wh.
Do I need a transfer switch?
For panel connections, approved transfer equipment is required.