About Size My Generator

SizeMyGenerator.com is a standalone informational website that helps homeowners plan for backup power.

Why it was created

Bill Christie created SizeMyGenerator to turn unfamiliar electrical loads and generator ratings into a practical starting point for a conversation with an installer. Bill has hands-on experience sizing, installing, and servicing residential HVAC systems.

Who operates the site

SizeMyGenerator.com was created and is operated by Bill Christie. Contact Bill at bill@sizemygenerator.com.

About this calculator

This site helps homeowners ballpark a generator size using a simplified interpretation of the National Electrical Code (NEC) dwelling load method, tailored for residential optional standby systems.

How the calculator works (high level)

General lighting load: 3 VA/ft² of floor area you enter.
Small appliance & laundry circuits: 1,500 VA each.
Fixed appliances: nameplate running watts at 100%.
Demand factor: first 10 kVA at 100%, remainder at 40% for non-A/C portion.
Cooling vs heating: larger of A/C or heat added at 100% (with special handling for heat pumps + strip heat).
EV charging: Level 2 loads added at 100% based on breaker size.
Headroom: default 20% safety factor before rounding to a common generator size.

What this site is (and isn’t)

This tool is oriented to residential optional standby systems (NEC Article 702). It is not intended for emergency systems (Article 700), legally required standby (Article 701), or critical operations power systems (Article 708), which have different requirements.

The result is a planning recommendation, not electrical engineering, an installation design, or approval by a manufacturer, utility, or authority having jurisdiction (AHJ). Before purchasing or installing a generator, have the final generator selection, transfer equipment, wiring, fuel supply, permits, manufacturer requirements, and local-code compliance confirmed by the appropriate qualified professionals.

Independence

The site currently has no display advertising, affiliate links, sponsored placements, or paid provider listings. See the Privacy Policy for how form information is handled.

Corrections & updates

We periodically review load tables and assumptions. If you spot anything off—or have a suggestion—please email us.