How our robot mower comparisons are researched

Where specifications come from

We display lawn capacity only when the exact listing states acres or square feet (square feet converted at 43,560 sq ft per acre), slope only with an explicit percentage next to slope wording, and wire-free or navigation wording only when the seller states it. A stated capacity is the seller’s coverage figure, not a measured mowing result. These attributes determine buyer-intent eligibility, not invented performance bonuses. The numeric evidence component uses the documented completeness formula below consistently across the catalog.

Each extracted attribute retains its source phrase. Unknown values remain unknown; a model number such as 3000 or 1500 is never read as a capacity. We do not calculate mowing time from capacity or battery figures.

Documentation component

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. These exact-ASIN stored listing inputs describe how much documentation is available, not measured mowing performance.

The same documentation component applies to all eligible mowers. Wire-free wording and stated capacity determine membership in their respective shortlists, not a performance bonus.

Review evidence and eligibility

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 captured public review data use the documentation score alone. This combined index reflects the public Amazon reputation and the listing documentation — it is not a physical test and not our own product testing.

Ranked comparators require complete robot mowers with an exact-ASIN captured average and positive review count. Accessories, boundary wire, blades, garages, named bundles and renewed listings are excluded from these rankings. The wire-free page additionally requires explicit no-perimeter-wire wording and the large-lawn page a stated capacity of at least 0.5 acre. Amazon may share reviews across variants: an exact-ASIN page count does not prove every review concerns only that configuration. Missing review evidence is not a zero-customer claim.

Displayed rating and order

The displayed editorial rating is the raw blended score divided by 10, shown to one decimal on a 0-10 scale. There is no catalog normalization, rank interpolation, forced winner, forced floor or artificial gap. Equal scores remain equal: the available data does not justify a distinction. Ranking uses the unmodified raw score descending, then listing slug for exact ties; slug is a stable identifier, not a quality signal. The same raw score always has the same display rating in every shortlist. This is not a physical test result or an Amazon customer rating.

Known variants share a model-family identifier and appear at most once per shortlist. The score is not a claim of best value, safety, measured cut quality or long-term reliability.

Lawn coverage planner

Lawn acres equal square feet divided by 43,560, the US survey acre. Margin equals (stated capacity − lawn acres) ÷ stated capacity × 100. An 8,000 sq ft lawn against a stated 0.25-acre capacity gives a 26.5% margin; a 0.5-acre lawn against a stated 0.37-acre capacity exceeds capacity by 35.1%. The optional slope check compares two percentages you enter. This arithmetic uses no assumed mowing speed, frequency or grass type and does not recommend, test or rank any model.

Freshness and illustrations

Offer and merchant-photo records are hidden when expired, with a maximum 24-hour lifetime from capture. We do not renew timestamps without a fresh authorized retrieval. Public review observations retain their original dates. Editorial illustrations are labeled and are not product photography or proof of testing.

Consult the exact manufacturer manual for base-station placement, boundary wire installation, blade replacement and supervision around children and pets. Never use a generated scene as a setup diagram. Read the buying guide or use the lawn coverage planner.

Publisher-assigned rating of the first-ranked listing

On each comparison page, the first-ranked listing may display a publisher-assigned editorial rating (publisher_assigned) instead of the formula result. Elias, the publisher, assigns this value manually; it is a subjective editorial judgment, not the output of the Amazon-review formula, not an Amazon customer rating and not a physical test result. The assigned value is between 9.1 and 9.4 and is stepped from the listing's unchanged formula score: 9.4 when the raw score is 88 or more, 9.3 for 84 to 87, 9.2 for 80 to 83 and 9.1 below 80. Where the formula already yields a displayed rating above 9.0, no exception is applied and the first-ranked listing shows the formula result. Every other listing on the page shows the formula result (formula_calculated). The exception replaces only the displayed rating on its named comparison; raw scores, Amazon review evidence, shortlist eligibility and order are unchanged. Each comparison page identifies its assigned rating in its method section, and the rating badge carries a data-rating-origin attribute naming its origin.

Spec-based ratings

Products without enough customer-review data still get our rating, built only from the exact Amazon listing. We score four criteria from 0 to 10: key specifications for the product type, stated build quality, warranty and certifications, how completely the listing documents what a buyer needs, and how clearly it states fit and compatibility. The rating runs from 4.5 to 8.5: 4.5 + the average of the four × 0.4. A thin listing lowers the rating but never below 4.5, because a short listing is not proof of a poor product; the 8.5 cap means that, without customer evidence, a product cannot outrank the review-backed picks of our comparisons. These are editorial judgments from documented facts, not hands-on tests, and they are labelled "Spec-based" wherever they appear.