Convert m to ft

The metre has been defined since 1983 as the distance light travels in 1/299,792,458 of a second. It is not a physical object any more; the platinum bar in Paris was retired.

A foot is twelve inches, and it is the unit heights and room sizes are quoted in across the United States. Aviation quotes altitude in feet almost everywhere, including in countries that are metric for everything else; China is the exception, where controllers clear aircraft in metres.

The factor is 3.28084, and almost nobody carries that around. Rounded to 3.3 it is off by 0.58 % — which stays invisible on small numbers and turns into a whole unit somewhere around 1,000 m.

That is the number worth knowing before you round: not the error itself, but where it stops being ignorable. Below that point the shorter factor is the sensible one; above it, use the field above, which never rounds until it prints.

The foot has been defined in metric terms since the international yard and pound agreement of 1959, and in this page's units that comes out at 0.3048 m to one. The definition is exact by stipulation — it was not measured, and it cannot be refined by measuring it better. The decimal above is the whole of it, with nothing rounded away at the end.

Before that agreement the US and the British versions differed slightly, and old survey figures still carry the older definition. For anything outside land surveying the difference is far below the precision anybody is working to.

The single most useful thing to carry away from this conversion is the anchor: one metre is 3.28084 feet, which is three feet and 3.37 inches. Anything built on that is close enough to talk with. Three metres is a shade under ten feet, so a room with a three-metre ceiling is a room with a ten-foot ceiling as far as any conversation is concerned. Two metres is six foot seven.

The reason the anchor works is that the error from calling a metre 3.28 feet is 0.03 per cent, which is under a centimetre over thirty metres. For a room, a doorway or a person that is far below the precision the original figure carried. Reach for the field above when the number is a specification and for the anchor when the number is a description.

A person 1.83 m tall is 6.0039 feet and is described as six foot. A person 1.75 m is 5.7415 feet and is five foot nine, because 0.7415 × 12 is 8.9 inches. The decimal is arithmetically right and conversationally useless, and the second step — multiply the remainder by twelve — is the one the calculator above does not do for you in words.

The trap is reading the decimal as inches. 5.9 feet is not five foot nine; it is five foot eleven, because nine tenths of a foot is 10.8 inches. That confusion is stable enough that spreadsheets holding heights as 5.9 and 5.10 sort them in the wrong order, and it is the reason a converted height is worth writing out in words rather than left as a number.

A metric building is dimensioned in round metres and an American one in round feet, and they land close together without meeting. The common metric ceiling is 2.4 m, which is 7 feet 10.5 inches against an American eight-foot ceiling at 2.438 m. A generous metric ceiling of 2.7 m is 8 feet 10 inches; a three-metre one is 9 feet 10.

Doorways run the same way. A metric door head at 2.04 m is 6 feet 8.3 inches and one at 2.1 m is 6 feet 10.7, against American openings at a round 6 feet 8 or 7 feet. None of these differences is large and all of them are visible: a wall unit, a door lining or a run of skirting made for one comes up short or long in the other, and the conversion is what tells you by how much before anything is ordered.

A height restriction is the one conversion on this page where the direction of the rounding is a safety decision. British bridge and barrier signs post the limit in metres with feet and inches underneath, and the imperial figure is rounded down rather than to the nearest: a 4.4 m clearance is 14 feet 5.2 inches and the sign reads 14 feet 5. Rounding up by a fifth of an inch would make the sign promise clearance that is not there.

The same rule applies to any converted figure that describes a maximum. Car park headroom of 2.0 m is 6 feet 6.7 inches, and quoting it as 6 feet 7 is a claim the structure does not support. Convert exactly, then round in the direction that makes the number more conservative — down for a clearance, up for a required height — rather than to whichever value looks tidiest.

A surprising number of metric sporting dimensions are rounded conversions of imperial originals, and converting them back makes the ancestry obvious. A football goal is 2.44 m high and 7.32 m wide, which are 8 feet and 8 yards. A men's high hurdle is 1.067 m, which is 42 inches, or 3 feet 6, to the nearest millimetre. A basketball hoop is specified at 3.05 m, two millimetres above the American ten feet at 3.048 m.

Others are genuinely metric and convert to nothing tidy. A high jump of 2.45 m is 8 feet and half an inch; a pole vault of 6.2 m is 20 feet 4 inches; a diving platform of 10 m is 32 feet 9.7 inches. The test is whether the imperial answer lands on a round number: if it does, the metric figure is a translation and the imperial one came first, which is worth knowing before deciding which of the two to treat as exact.

From 1959 until the end of 2022 the United States had two feet. The international foot is exactly 0.3048 m; the survey foot was 1200/3937 m, about 0.30480061 m, and it was kept because a century of surveying, state plane coordinate systems and published elevations had been computed with it. The two differ by two parts per million, which across a room is a hundredth of a millimetre and completely undetectable at the scale this page converts at.

It is not undetectable at survey scale. A state plane coordinate runs to millions of feet, and two parts per million on a million feet is two feet on the ground — enough to move a property line. The National Geodetic Survey and NIST retired the survey foot on 31 December 2022, so anything measured since then uses the international foot; anything older, particularly an elevation or a coordinate, may not, and the source has to say which.

The conversion is exact in the sense that the factor is fixed, and the digits it produces are more than the input usually deserves. A room height given as 2.4 m is a nominal figure rather than a measurement, and converting it to 7.874 feet claims a thousandth of a foot that was never present. Round the answer to match the input rather than to match the calculator.

A useful rule at this scale: a figure given to the nearest centimetre supports feet and inches to the nearest inch, because an inch is 2.54 cm. A figure given to the nearest millimetre supports a tenth of an inch. A figure given to the nearest tenth of a metre — which is what most quoted room and ceiling heights are — supports feet alone, and the inches after it are arithmetic rather than information.