Area is where a rounding error doubles. Every factor here is a length factor squared, so a figure that is a tenth of a percent out in metres is two tenths out in square metres, and on a floor plate or a field that is a room or a paddock. Two of these units are exact and two are not, and the difference is worth knowing: the square foot and the square inch follow from the international foot of exactly 0.3048 metres, so their factors carry no rounding at all. The acre does not. It is a survey unit inherited from ploughing, its published value is printed to seven figures rather than defined, and it exists in two slightly different versions depending on which foot the survey used. The hectare sits on the other side of that line — exactly ten thousand square metres, a square a hundred metres on a side, with no history to argue about. Every converter here marks which case it is in rather than presenting all four as equally solid.
Tools in this category
Square Feet to Square Meters
Convert square feet to square meters exactly. A square foot is 0.09290304 square meters, which follows from the foot being exactly 0.3048 metres.
Square Meters to Square Feet
Convert square meters to square feet by dividing by the exact factor, not by multiplying by a rounded 10.76. Runs entirely in your browser.
Acres to Hectares
Convert acres to hectares. A hectare is exactly 10,000 square metres; the acre is not exact, and this page says which acre it uses.
Hectares to Acres
Convert hectares to acres. The hectare is exact, the acre is not, and the result is marked as rounded rather than presented as exact.
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How these tools are built
Every tool in this category runs entirely in your browser: there is no upload, no account and no request to a server once the page has loaded. The numbers behind them are transcribed from the organisation that defines them — NIST for units, the W3C for web formats, the WHO for health measures — and each page names its source next to the formula. A tool whose reference values stop reproducing fails the build and does not ship, which is the whole reason the catalogue grows slowly.