How this instrument works
The conversion rests on a single agreed number. In 1959 the standards laboratories of six English-speaking nations fixed the international yard at 0.9144 metres exactly, which makes one foot — a third of a yard — exactly 0.3048 metres. Nothing is measured and nothing drifts: multiply a length in feet by 0.3048 and you have metres, correct to as many digits as you care to carry.
The opposite direction is less tidy. One metre is 1 ⁄ 0.3048 feet — the fraction 1250⁄381 — whose decimal expansion 3.280839895013123… never terminates. This sheet carries the factor to sixteen figures, far beyond the resolution of any tape measure, and rounds only at the display. For rough work, 3.28 feet per metre lands within three hundredths of a percent.
One historical wrinkle deserves a note. American land surveys long used a slightly different foot, defined as 1200⁄3937 metres — about two parts per million longer than the international foot. NIST retired the U.S. survey foot at the end of 2022, so the value used here is now the only foot in official service. The metre itself is spelled meter in the United States; the length is identical.
- Set the dial to the direction you need: 'm to ft' to start from metres, 'ft to m' to start from feet.
- Type your length into the live field — Metres in the first mode, Feet in the second.
- Read the converted value below; both named fields stay in step, so the reverse reading is already on the sheet.
- Adjust the figure and watch the result track it — four decimal places are kept throughout.
Worked example — the 10-metre diving platform
The top board at an Olympic pool stands 10 metres above the water. In feet: 10 × 3.280839895 = 32.808399 ft, which the sheet displays to four decimals as 32.8084. Divers who train in imperial units call it the 33-foot platform, rounding up by a hand's width — the leftover 0.8084 ft is 9.7 inches.
Run it backwards as a check. Switch the dial to 'ft to m' and enter 32.808399: the instrument returns 32.808399 × 0.3048 = 10.000000 metres, the original figure to the last digit — exactly what an exact definition, applied in both directions, must do.
Questions
How many feet are in one metre?
3.280840 feet, to six decimals — in carpenter's terms, about 3 feet 3⅜ inches. The exact value is the fraction 1250⁄381, whose decimal 3.280839895013123… never ends. For mental arithmetic, 3.28 is within 0.03%, and the old trick of adding ten percent then tripling gives 3.3 — about 0.6% high, fine for a glance at a ceiling.
Is the metres-to-feet conversion exact?
Feet to metres, perfectly: 0.3048 is the definition of the foot, so multiplying by it introduces no error at all. Metres to feet requires dividing by 0.3048, and that quotient is a never-ending decimal, so any written factor is a truncation. This sheet carries sixteen figures — an error of about a ten-thousandth of a nanometre over a full kilometre.
Why is a foot exactly 0.3048 metres?
Because six national laboratories agreed to make it so. Before 1959 the US, UK, Canada, Australia, New Zealand and South Africa each kept feet that differed by a few parts per million. The international yard and pound agreement fixed the yard at 0.9144 m exactly; a foot is one third of that, 0.3048 m, and it has been a defined constant — not a measured one — ever since.
What is the difference between the international foot and the US survey foot?
About two parts per million. The U.S. survey foot, defined as 1200⁄3937 m, runs roughly 2 mm longer per kilometre — irrelevant for a room, decisive for state-plane coordinates spanning counties. NIST and NOAA retired the survey foot after 31 December 2022; this instrument uses the international foot, 0.3048 m exactly, the only foot now in official use.
Can I use this factor for square metres or metres per second?
Square it for areas, cube it for volumes: 1 m² is 3.280839895² ≈ 10.7639 ft², and 1 m³ ≈ 35.3147 ft³. Speeds scale linearly, so 1 m/s is about 3.2808 ft/s. This dial converts plain lengths only — applying the single factor to an area is the classic mistake, and it leaves the answer short by a factor of 3.28.