Feet vs Meters

• 1The relationship is exact by definition, not measured: 1 ft = 0.3048 m precisely, set by the international yard and pound agreement of 1959.
• 2The US retains a second, very slightly different foot for legacy surveying — the US survey foot, 1200/3937 m — which differs from the international foot by about 2 parts per million. It was officially deprecated at the end of 2022, but it persists in older state plane coordinate data, where the difference matters over long distances.
• 3Aviation is the notable holdout: altitude is quoted in feet almost worldwide, including in countries that are otherwise fully metric, because international air traffic standardised on it. China, Russia and a few others use metres.
• 4Construction in the US uses feet and fractional inches; construction almost everywhere else uses millimetres, not metres, because millimetre dimensions avoid decimal points on drawings.
• 5Human height is stated in feet and inches in the US and UK, and in centimetres nearly everywhere else.

The foot descends from body-based measurement and varied widely across Europe before standardisation — a Roman foot, an English foot and a Parisian foot were all different lengths. The metre was defined in the 1790s as one ten-millionth of the distance from the equator to the North Pole, deliberately chosen to be independent of any monarch or body. The two systems were finally reconciled in 1959, when six English-speaking nations agreed to define the yard as exactly 0.9144 metres, making every imperial length unit a fixed multiple of an SI one.