Sizing calculator

How much backup power do you need?

Choose your devices, a backup window, and what you are planning for. Advanced electrical controls are optional.

POWER NEEDS

Scenario shortcuts

Add a device

Example planning values — edit them to match your actual devices.

DEVICE 1

Device name

Quantity

Running watts

Startup watts (optional)

Duty cycle (%)

Usage hours

May run simultaneously

Source: U.S. Department of Energy appliance tableUses a 50% cycling duty-cycle planning assumption. The 1,500 W startup value is a conservative 3× allowance, not a universal appliance specification. Verify the nameplate or manufacturer documentation.

DEVICE 2

Device name

Quantity

Running watts

Startup watts (optional)

Duty cycle (%)

Usage hours

May run simultaneously

Source: ENERGY STAR consumer-electronics market reportUses the upper end of the cited 5–10 W router range as a planning value.

DEVICE 3

Device name

Quantity

Running watts

Startup watts (optional)

Duty cycle (%)

Usage hours

May run simultaneously

Source: ENERGY STAR certified light-fixture listingExample certified LED fixture value; edit this to match the wattage printed on each lamp.

DEVICE 4

Device name

Quantity

Running watts

Startup watts (optional)

Duty cycle (%)

Usage hours

May run simultaneously

Source: U.S. Department of Energy-hosted plug-load studyRounded planning value based on a measured 57.5 W laptop example; use the charger label or a watt meter for your device.

DEVICE 5

Device name

Quantity

Running watts

Startup watts (optional)

Duty cycle (%)

Usage hours

May run simultaneously

Source: Apple 20W USB-C Power Adapter specificationsUses a maximum adapter output as a conservative planning value; actual charging draw usually varies over the charge cycle.

Primary use (required)

LOAD SUMMARY

Devices selected: 6
Estimated energy: 2,832 Wh
After conversion losses: 3,332 Wh
Recommended rated capacity: ~3,920 Wh+
Maximum simultaneous load: 609 W
Startup / surge requirement: 1,609 W

Energy uses each row’s runtime, quantity, and duty cycle. Output sums checked devices; unchecked devices are treated as one-at-a-time loads. Startup replaces that device’s running draw during its start event.

YOUR ESTIMATED NEED

Battery size

~3.9 kWh+

Power output

~609 W+

Startup capability

~1,609 W

See calculation details