644 feet per second in knots

Conversion

644 feet per second is equivalent to 381.559568034557 knots.^[1]

Conversion in the opposite direction

The inverse of the conversion factor is that 1 knot is equal to 0.00262082275947391 times 644 feet per second.

It can also be expressed as: 644 feet per second is equal to $\frac{1}{0.00262082275947391}$ knots.

Approximation

An approximate numerical result would be: six hundred and forty-four feet per second is about three hundred and eighty-one point five six knots, or alternatively, a knot is about zero times six hundred and forty-four feet per second.

Units involved

This is how the units in this conversion are defined:

Feet Per Second

'The foot per second (plural feet per second) is a unit of both speed (scalar) and velocity (vector quantity, which includes direction). It expresses the distance in feet (ft) traveled or displaced, divided by the time in seconds (s, or sec). The corresponding unit in the International System of Units (SI) is the metre per second.Abbreviations include ft/s, ft/sec and fps, and the rarely used scientific notation ft s−1.'

Wikipedia page of feet per second

Knots

"The knot (/nɒt/) is a unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph. The ISO Standard symbol for the knot is kn. The same symbol is preferred by the IEEE; kt is also common. The knot is a non-SI unit that is accepted for use with the SI. Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour. Etymologically, the term derives from counting the number of knots in the line that unspooled from the reel of a chip log in a specific time."

Wikipedia page of knots

Footnotes

[1] The precision is 15 significant digits (fourteen digits to the right of the decimal point).

Results may contain small errors due to the use of floating point arithmetic.