Generator Coverage Estimator
Choose what you must have, would like and don't need during an outage. Get an estimated generator range from your loads, not from the size of your house.
What do you actually want to keep running?
Sizing starts from your loads, not from the size of your house. Mark each one.
Generator sizing starts with what you want to keep running, not with the square footage of your house. Mark each load as must-have, would-like or not needed and this estimator returns a running-capacity planning range in kW, tells you which loads are driving it, and flags the starting surge that has to be added on top by whoever sizes the unit.
Have these to hand
- —The loads you genuinely need during an outage — heating, refrigeration, well or sump pumps, medical equipment, lights and internet before anything else.
- —Which large electric appliances you expect to use: dryer, range, water heater and central air conditioning are the four that drive capacity.
- —The fuel actually available at the property: natural gas, propane or diesel.
- —Whether sequencing large loads instead of running them together is acceptable to you.
How the range is calculated
- —The low end sums the running demand of your must-have loads. If you accept load management, only the largest capacity-driving load counts instead of all of them, because they are sequenced rather than carried at once.
- —The high end sums everything you marked must-have or would-like, running together with no sequencing.
- —Motor and compressor loads are identified separately. Their starting demand is far higher than their running demand and must be added on top of the range — the figures do not assume every motor starts at the same moment.
- —Fuel choice does not change the kW range; it changes supply sizing, tank capacity and refuelling, which is reported alongside the result.
What this estimator is not
- —It is not an electrical design or installation specification. Final sizing needs a load calculation against your actual panel and appliance nameplate data.
- —It does not choose a transfer switch. Whole-panel versus essential-loads configuration materially changes both cost and coverage.
- —It does not cover placement, clearances, noise limits or permitting, all of which are decided locally.
Common questions
Because two identical houses need very different generators depending on whether they have electric heat, a well pump and central air conditioning. Capacity follows the loads you keep running, so the estimator asks for those directly.
Load management sequences large loads instead of running them simultaneously, which lets a smaller unit serve more circuits. Accepting it lowers the bottom of your range; refusing it pushes the requirement toward the top.
No, and that is deliberate. The range is running capacity. The starting demand of your largest motor or compressor load is reported separately so it is added once, by whoever specifies the unit, rather than being buried in an estimate.
Where this fits in the decision
- What size generator do I actually need?
How capacity, surge and transfer switches interact.
- What should I actually power during an outage?
How to decide which loads belong on the must-have list.
- Generator or battery backup: which type do I need?
Worth reading before you size either one.
- Home Power & Technology
Standby generators, whole-home battery backup and portable power.