How this instrument works
France's Academy of Sciences launched the metre in 1791 as one ten-millionth of the meridian quadrant running from the North Pole to the equator through Paris — a survey between Dunkirk and Barcelona was meant to fix its length for good. It didn't. In 1889 the metre became a specific platinum-iridium bar kept near Paris; in 1960 it became 1,650,763.73 wavelengths of light from krypton-86; and since 1983 it has been the distance light travels, in a vacuum, in 1 ⁄ 299,792,458 of a second — a definition tied to a physical constant rather than an object or an emission line, and the first that seems built to never need changing again.
The foot, by contrast, only needed fixing once. Before 1 July 1959, American and British feet differed by a hair: the US foot, set by an 1893 order equating one metre to 39.37 inches exactly, worked out to about 0.3048006 m, while Britain's own imperial standard landed fractionally differently again. The 1959 international yard and pound agreement erased the gap by fixing the yard at 0.9144 m exactly, making the international foot — a third of that yard — exactly 0.3048 m everywhere. America kept its old, very slightly longer 'US survey foot' for land-survey coordinate systems until the National Geodetic Survey and NIST formally retired it at the start of 2023.
Feet also survive in places metric countries never expected. Olympic platform diving's highest board sits exactly 10 m above the water, a figure broadcasters routinely round to 'about 33 feet' for English-speaking audiences. Commercial aviation cruises at altitudes given in feet — 35,000 ft is a familiar cruising level — even over countries that otherwise use metres for everything else, because international aviation adopted feet for altitude worldwide and never switched.
- Enter a height or length into the Metres (m) field. It starts at 10, the height of an Olympic diving platform.
- Read the Feet (ft) field, recalculated to eleven decimal places with every keystroke.
- Converting feet back to metres? Multiply by 0.3048 — that direction is exact, with nothing to round.
- For a quick estimate, multiply metres by roughly 3.28, then refine with the full factor for anything precise.
Worked example — a 10 m Olympic diving platform
Enter 10 into Metres (m) and Feet (ft) reads 32.8083989501. Olympic and World Aquatics platform-diving events set the highest board at exactly 10 m above the water — a figure fixed in the sport's rules, not an approximation — and English-language broadcasts commonly round that to 'about 33 feet' for viewers more familiar with imperial heights.
The gap between the rounded '33 ft' and the true 32.8083989501 ft is a little under two and a half inches, easily lost in a headline but not in engineering drawings for the platform itself, which are specified in metres regardless of which unit gets announced on air. Divide 32.8083989501 by 3.28083989501 and the answer returns to exactly 10, with no rounding lost along the way.
Questions
Why has the metre been redefined multiple times but the foot only once?
The metre chased ever-higher precision across two centuries — from a meridian survey to a metal bar to a light emission line to today's speed-of-light definition — because each older method eventually hit a measurement limit. The foot, by contrast, was simply reconciled between countries in 1959 by fixing the yard at 0.9144 m; it hasn't needed redefining since because it was never trying to track a physical constant in the first place.
Is the metre still connected to Earth's meridian at all?
Only historically. The 1791 definition — one ten-millionth of the distance from the North Pole to the equator through Paris — was abandoned once the original survey proved slightly inaccurate and better methods became available. Today's metre is defined through the speed of light and has no direct tie back to Earth's actual shape.
How many feet are in a metre, precisely?
Exactly 3.28083989501 ft, the reciprocal of 0.3048 m carried to twelve significant figures. Because 0.3048 has no clean relationship to a base-ten fraction, the reverse ratio never terminates — this calculator simply carries it further than most everyday conversions bother to.
Why doesn't 1 metre equal a round number of feet and inches?
Because the metre and the foot were defined independently, in different eras and different countries, and only reconciled by international agreement in 1959. A metre works out to 3 ft 3.37 in — not a tidy figure — simply because nothing about their separate histories was designed to align.
What is the US survey foot, and does it still matter?
It was a very slightly longer American foot, about 0.30480061 m, based on an 1893 rule equating one metre to 39.37 inches exactly, kept alive after 1959 specifically for land-survey coordinate systems. The National Geodetic Survey and NIST formally retired it at the start of 2023, so current US mapping and legal surveys now use the same international foot as everyone else.
Why do pilots still use feet for altitude worldwide?
International aviation standardised on feet for altitude reporting decades ago, and safety depends on every pilot and air traffic controller using the same reference regardless of which country's airspace they're in. Switching a global, safety-critical convention carries far more risk than any benefit from matching a country's everyday metric units, so feet have simply stuck.