Advertising. Some links go to Amazon search. No Associates tracking tag is attached. If one is approved and added later, BlackoutSmart may earn a commission. Safety advice and specifications do not depend on those links. Full affiliate disclosure.

Updated 2026-11-07

Home / Calculator

Runtime calculator

Usable Wh = capacity × depth of discharge × inverter efficiency. Runtime = usable Wh ÷ average load. Average load = running watts × duty cycle + idle draw. Continuous and surge checks use the numbers in the form.

Model from the database Choosing a model fills only the fields the spec record actually has.

Appliance presets

Each preset writes assumption numbers you can edit. It does not claim BlackoutSmart measured the appliance.

No preset selected.

Capacity (Wh) Watt-hours only. A milliamp-hour rating is not converted. Depth of discharge (%) Default 90% is a planning assumption. None of the model records include a manufacturer recommended depth of discharge. Inverter efficiency (%) Default 85% is a planning assumption. Use 100 only for a USB or DC load that does not pass through an AC inverter. This site has no measured efficiency for these models. Idle draw (W) Filled from a manufacturer standby figure when the record has one. Otherwise zero is your assumption, and it makes the runtime look longer. Running watts Starting watts Used for the surge check. Leave blank if you do not have a starting figure. Duty cycle (0 to 1) 1 means the load runs the whole time. 0.3 means it runs 30% of the time, which is a common planning assumption for a fridge compressor, not a measurement. Continuous rating to check (W) Surge or peak rating to check (W) X-Boost or SurgePad marketing numbers are not filled in here unless the model record stored them as the surge field. Most of those modes are documented separately and left out of this box.

How does the formula work?

What formula does the calculator use?

Usable watt-hours equal capacity times depth of discharge times inverter efficiency. Average load equals running watts times duty cycle, plus idle draw. Runtime equals usable watt-hours divided by average load.

Are the appliance presets measurements?

No. Each preset is a labeled planning assumption. Replace the watts with the figure on your appliance nameplate. Fridge presets include a duty cycle because compressors do not run the whole time. That duty cycle is an assumption, not a test of your fridge.