Methodology: wattage pairs, fuel support and listing provenance

Ranking fuel-burning generators honestly starts with an admission: we work from listing documentation, not from a test bench. Nothing below is a measurement of ours. What we promise instead is that every number has a traceable origin in the exact Amazon listing it describes, and that every formula between that origin and a displayed rating is published on this page.

Extraction before scoring

For each generator we scan the listing title, then the feature bullets, for running (rated) watts and peak (starting/surge) watts stated with an explicit wattage term. A bare wattage in a product name is read as the peak figure, the near-universal convention in generator marketing. Fuel support — gasoline, propane, natural gas — is taken from the listing text alone. Each extracted attribute stores its source location, and a listing that never states both watt figures explicitly is scored on documentation completeness instead of spec fit; we do not fill gaps by analogy with similar models.

The three formulas

Documented spec fit = 100 × [0.45 × min(running watts / 9,500 W, 1) + 0.35 × min(peak watts / 12,500 W, 1) + 0.20 × min(supported fuel count / 3, 1)], rounded to a whole number. Running and peak watts require explicit roles and units in the exact listing or linked documentation for the exact manufacturer model; manufacturer values here are for gasoline. Bare marketing wattage is not treated as peak output; contradictory values are omitted, not swapped; the fuel count reflects gasoline, propane and natural gas support the listing itself claims. This index summarizes listing documentation for outage sizing — it is not a load test, a noise measurement or a durability judgment.

Documentation completeness = 100 × [0.5 × min(feature bullets / 8, 1) + 0.3 × min(listing images / 5, 1) + 0.2 × (brand stated ? 1 : 0)], rounded to a whole number, computed from the stored Amazon listing record when the listing text does not state both running and peak watts explicitly. It measures how completely a seller documents a listing — nothing about how the generator performs.

Where Amazon publicly displays customer reviews for a listing (average star rating and review count captured from the public product page), the raw editorial score is 100 × [0.45 × (Amazon average / 5) × min(review count / 50, 1) + 0.35 × min(log10(1 + review count) / log10(1 + 5000), 1) + 0.20 × documentation score / 100]. The confidence factor min(review count / 50, 1) damps averages based on very few reviews, and the logarithmic volume term rewards large public review volumes, so widely and highly reviewed listings rank ahead of thinly reviewed ones. Listings with no verified public review data use the documentation score alone in the catalog and are excluded from comparator shortlists. Comparator publication requires at least five review-backed eligible listings per pool. This combined index reflects the public Amazon reputation and the listing documentation — it is not a physical test and not our own product testing.

From raw score to displayed rating

The displayed editorial rating is the raw 0–100 score divided by ten, shown to one decimal on a 0–10 scale. We do not normalize against the catalog, force endpoints or alter decimals by rank. Genuine ties remain visible; equal raw scores are ordered by listing slug for stability. This is an editorial index, not a physical test or an Amazon customer rating.

Within each comparison list, displayed values strictly decrease wherever raw scores differ, so the visible order always tells the same story as the underlying arithmetic.

Boundaries we hold

Standby generators requiring professional installation are excluded from the catalog entirely. No comparison on this site crosses the combustion/battery boundary — the two classes answer different questions, as our guide article explains. Prices, stock and review counts render only from data fetched within its 24-hour validity window, and never appear baked into a page. Noise, vibration, cold-start behavior and long-term durability are real buying factors we simply cannot score from listings — which is why every rating here is labeled an index of documentation, never a verdict on the machine.

Corrections

Spotted a wattage we misread or a fuel claim that drifted? Write to [email protected] with the page URL and the listing text; provenance records make these checks fast. The affiliate disclosure covers the commercial relationship.