The exact figure
Again a consequence of the 1959 yard definition: a foot is a third of a yard, and 0.9144 divided by three is exactly 0.3048. The roughly 3.28 in the other direction is the awkward one to remember, which is why most people convert metres to feet by multiplying by three and adding a bit.
A useful mental anchor: three metres is just under ten feet, off by about 1.6 inches. For rough work, treating a metre as 3 feet 3 inches is accurate to within a quarter of an inch.
Feet and inches are not decimal feet
This is the error that ruins conversions. A height of 5 feet 10 inches is not 5.10 feet. Inches are twelfths, so 10 inches is 10/12 of a foot, making the height 5.8333 feet, which converts to 1.778 m.
Treating it as 5.10 feet gives 1.554 m — wrong by more than 20 centimetres, which is the difference between a short adult and a tall one. The rule is to divide the inches by twelve before converting, or convert the whole height to inches first and use the inches conversion instead.
For reference, 5 foot 6 is 1.676 m, 5 foot 10 is 1.778 m, and 6 foot is 1.829 m.
Aviation kept feet, and mostly for safety
Altitude is measured in feet across most of world aviation regardless of the country's ground-level units, with China, Russia and a few neighbours as the main exceptions. Cruising altitudes are quoted as flight levels — FL350 means 35,000 feet on a standard pressure setting, which is about 10,668 m.
The persistence of feet here is not sentiment. Vertical separation between aircraft is defined in feet, altimeters worldwide are calibrated in feet, and a mixed system creates exactly the kind of unit-confusion accident that aviation spends enormous effort avoiding. The cost of switching outweighs the elegance of consistency, so feet stayed.
Where the numbers get large
Building heights, mountain elevations and diving depths all attract this conversion, and at those magnitudes the rounding matters. Mount Everest at 8,848.86 m is 29,031.7 feet, and the familiar 29,029 figure comes from an earlier survey rather than a different conversion.
A useful check on any large conversion: metres to feet should roughly triple the number. If your answer has not grown by about a factor of three, the direction is inverted — the single most common mistake in this pair, and one the swap button above exists to prevent.
Frequently asked questions
How many metres is 6 feet?
1.8288 m exactly, since a foot is exactly 0.3048 m. For quick mental work, 6 feet is a shade over 1.83 m.
How do I convert 5 feet 10 inches to metres?
Convert the inches to a fraction of a foot first: 10 inches is 10/12, so the height is 5.8333 feet, which gives 1.778 m. Treating it as 5.10 feet gives 1.554 m, which is wrong by over 20 cm.
Why does aviation still use feet for altitude?
Altimeters worldwide are calibrated in feet and vertical separation rules are defined in feet. A mixed system would introduce exactly the unit-confusion risk aviation works hardest to eliminate.