Civil-Environmental Engineering

Handy Facts:

(1) Acre=43560 sf               Why such an odd number?

The fundamental unit of land measurement in the US is the 'Township' (taken from the old English 'Parish').  A Township is 6 miles on a side, and is divided into sections, each one mile on a side.  These are divided in half along each side to create quarter sections, then divided again the same way to create 4 parcels, each of 40 acres.  So for each quarter section there are two "Front 40's"​ and two "Back 40's", which is where the term 'the back 40' came from.  That makes an acre:

(5280 ft/mi /2/2) x (5280 /2/2) / 40=43560 sf.    An odd-ball number, but there it is.

(1) cubic foot=7.48 gal.          How can I remember this?

 

Picture a one-gallon milk jug.  You can take four of them and set them together to make a square, if you turn them so the handles are sticking on the outside of the square.  Now, if you put a piece of cardboard on them, you could stack on four more.  That would be 8 one-gallon jugs in a space just one foot by one foot square, by one foot high; one cubic foot, in other words.  But of course the handles are sticking out, so take off a half gallon for them and you get 7.5 gallons in a cubic foot.  That's within 1/4 of one percent (0.25%).  Not bad.