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Generator Size Calculator

Find the generator size your home needs — running watts plus motor starting surge, sized to a real standard generator — with U.S. pricing, fuel cost for an outage, a size comparison, and a downloadable PDF load list.

Wattages are typical U.S. averages — check the nameplate on your own equipment. Motors (AC, well pumps, compressors) draw a large starting surge. Estimates use 2024-2025 U.S. prices. For planning purposes only — a licensed electrician must size and connect a standby unit.

Loads & Generator
1 What You Want To Power
Presets tick the list below — then add or remove anything you like.
0 items selected
watts
Anything not on the list — medical equipment, shop tools, a second fridge.
2 Generator & Fuel
25%
20-25% is standard. Never run a generator at 100% load for hours.
60%
Not everything runs at once. 50-70% of your running watts is typical — drives fuel use.
hours
Used to estimate fuel burned and fuel cost.
3 Equipment & Fuel Cost
$/ kW
Portable ~$150-250/kW, inverter ~$350-500/kW, air-cooled standby ~$350-500/kW.
$total
Standby install (pad, gas line, ATS, permit) ~$3,000-$8,000. Portable interlock kit ~$150-600.
$/ therm
U.S. residential natural gas ~$1.10 - $1.70 per therm.
Generator Estimate
Recommended Generator Size
—
Pick the loads you want to power
Running Watts —
Peak Starting Watts —
Headroom At This Size —
Full Cost Breakdown
Required capacity —
Generator unit —
TOTAL ESTIMATE—
Fuel use / hour —
Fuel for outage —
Upfront (unit + install) —
Cost Breakdown Chart
Estimated cost by category ($)
Size Comparison — Your Load
SizeContinuous WattsSurge WattsHeadroomEst. Unit Cost

For your 0 W running load and 0 W peak surge, at $400/kW. Surge column assumes a 1.25× starting rating.