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The acre is an imperial unit of area.
One acre is equal to an oblong measuring $1$ chain by $1$ furlong.
That is, measuring $4$ rods, poles or perches by $10$ chains.
|\(\ds \)||\(\)||\(\ds 1\)||acre|
|\(\ds \)||\(=\)||\(\ds 4\)||roods|
|\(\ds \)||\(=\)||\(\ds 10\)||square chains|
|\(\ds \)||\(=\)||\(\ds 160 = 4 \times 40\)||square rods, poles or perches|
|\(\ds \)||\(=\)||\(\ds 4840 = 22 \times 220\)||square yards|
The acre is a traditional measure of land arising from the days of ploughing in mediaeval times and earlier.
It was defined as the area of land that could be ploughed by $1$ ploughman with $1$ ox in $1$ day.
It is noted that an acre is not actually defined as a square area, but as an oblong strip $10$ times as long as it is wide.
The reason is readily apparent: its length is, as is apparent from its definition, one furlong, that is, furrow-long.
The word acre derives from the Old English æcer, meaning open field.
It is pronounced ay-ker, and was at one time spelt aker.
- 1944: Alfred E. Holbrow: Geometrical Drawing (12th ed.) ... (previous) ... (next): Section $\text I$. Introduction
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $4840$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $4840$
- 2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) ... (previous) ... (next): acre