How this instrument works
A metre stopped being a bar of metal in 1983, when CGPM redefined it as whatever distance light covers in vacuum during 1/299,792,458 of a second. Feet inherit that definition at one remove. In 1959, six national standards bodies — American, British, Canadian, Australian, New Zealand and South African — signed an agreement fixing one yard at 0.9144 m, and with it one foot at 0.3048 m. That number was never measured. It was negotiated, then written into law.
Invert 0.3048 and you get 1250⁄381, an ordinary fraction, since 0.3048 is 381/1250. Its decimal form, 3.280839895013123…, never terminates; it repeats on a 42-digit cycle, because 381 factors as 3 × 127 and 127 runs a long period in base ten. This converter stops at eleven decimals. Truncating there costs about 3 × 10⁻¹² ft per metre — under one nanometre spread over an entire kilometre, far below what tapes, EDM instruments or laser trackers could ever resolve.
Feet persist wherever metrication stalled or was never demanded. Airliners nearly everywhere report altitude in feet, so FL350 means 35,000 ft, yet Chinese airspace assigns cruising levels in metres and crossing crews convert in flight. American builders quote ceiling heights, lumber and floor area in feet; British building regulations run in metres, though a Scottish summit earns Munro status only above 3,000 ft, or 914.4 m. Charts split along national lines too: Admiralty depths in metres, plenty of NOAA soundings still in feet.
- Type your measurement into Metres (m). It opens at 10 m so you can see a live answer straight away.
- Read Feet (ft) directly below; it recalculates on every keystroke, with no button to press.
- Want feet and inches? Keep whole feet as they stand, then multiply what remains after that decimal point by 12.
- Working backwards from a figure in feet, multiply by 0.3048 to recover metres, then type that into Metres (m) to check yourself.
Worked example — a 10 m diving platform
Olympic platform diving happens from 10 m. Enter 10 into Metres (m) and Feet (ft) returns 32.8083989501. Commentators habitually call that 33 feet, which flatters every dive by more than two inches.
Convert that decimal properly and 0.8083989501 ft × 12 gives 9.70 in, so a platform sits 32 ft 9.7 in above water. Anyone reading .80 as eight inches lands 1.7 in low — a slip that reaches drawings and spec sheets far more often than it should.
Questions
Is 3.28083989501 an exact figure?
No, it is rounded. Exactly, one metre equals 1250⁄381 ft, whose digits run 3.280839895013123… forever. Exactness lives in reverse: 1 ft = 0.3048 m by definition, agreed in 1959 and unchanged since. Stopping at eleven decimals leaves roughly 3 × 10⁻¹² ft of shortfall per metre, which amounts to under one nanometre across one kilometre — nothing you could detect with any field instrument.
How do I turn a decimal answer into feet and inches?
Multiply whatever follows that decimal point by 12, never by 10. From 32.8083989501 ft, keep 32 ft and take 0.8083989501 × 12 = 9.70, giving 32 ft 9.7 in. Reading .80 ft as "eight inches" is a genuinely common error and it lands you nearly two inches short. For carpentry, round those inches to a sixteenth: 9.70 in is 9 11⁄16 in, near enough to scribe.
Is a US survey foot different from this foot?
Yes, slightly, and it no longer belongs in new work. A survey foot measures 1200⁄3937 m, roughly 0.30480061 m, about two parts per million longer than an international foot. NIST and NOAA retired it on 31 December 2022. Across one room that gap vanishes; across State Plane coordinate grids it grows into metres, so legacy survey data should be labelled before anyone converts it.
Do imperial feet and US customary feet differ?
Not since 1959 — both measure 0.3048 m, so a British foot and an American foot are one unit under two names. Divergence between imperial and US customary shows up in volume instead: a US pint holds 473 mL against an imperial 568 mL, and gallons differ by a fifth. Length, area and altitude convert identically on either side of the Atlantic; drinks and fuel do not.
Can I just multiply by 3.28 in my head?
For rough work, yes. Using 3.28 undershoots by about 0.026%, which over 100 m loses only 0.084 ft, near enough an inch. A neater mental trick: triple your metres, then add ten per cent, since 3.3 sits within 0.6% of truth. Both shortcuts fail once tolerances tighten — steelwork, aviation clearances, survey traverses — where full precision belongs.
Why do aircraft report altitude in feet at all?
Because aviation grew up around American and British instruments, and ICAO permits feet for vertical position as a non-SI unit in continued use. Altimeters, terrain databases and separation minima are all built around 1,000 ft steps, so replacing them costs far more than tolerating one imperial holdout. China and a handful of former Soviet states kept metric levels, which is precisely why crews flying into Chinese airspace carry conversion tables.