It sounds like one of those questions you ask only when you're either four years old or unbelievably high:
"What's that?" "That's a pound of sugar." "Why?"
"Have you ever looked at a meter? I mean, really looked at it?"
These- and others- are measurements that are ubiquitous in our lives, used as frames of reference for anything and everything. But they didn't just pop up out of thin air. There's a reason why a pound is that amount of weight, or a gram. There's a reason a meter or a foot or a mile is that distance.
So, what are you really measuring?
INCH: A lot of the smaller units of length in the imperial system- the one the United States uses and pretty much nobody else nowadays- were based on measuring the human body. After everyone using their own bodies as measuring sticks led to a lot of confusion over exact amounts, standardized lengths were settled upon. For the inch, in 1324 King Edward II decided that the inch would be three barleycorns placed end-to-end.
FOOT: The average length of a man's foot, naturally.
YARD: The length from the tip of a man's nose to the end of his outstretched arm. Or, more accurately, the tip of Henry I's nose to the end of his thumb. In 1844 the British government created a 'master' yard, marked off in feet and inches, that would serve as the standard. One such master sits here in Trafalgar Square.
FATHOM: Both outstretched arms, defined by Parliament as "the length of a man's arms around the object of his affections." Later standardized to six feet.
FURLONG: The distance a team of oxen could plow without resting.
ACRE: A furlong squared, except you don't have to actually square it, because the plow got ornery too often.
MILE: One thousand double paces, or more to the point, two thousand paces. Queen Elizabeth I placed it at 5,280 feet in 1592, which is eight furlongs.
METER: One ten-millionth of the distance from the North Pole to the Equator, at least as far as they figured it in 1795. They messed it up a bit. They got around to fixing that mess-up in 1983, when the meter was redefined as the distance light in a vacuum travels in one 299,792,458th of a second. There's probably a mnemonic for that.
OUNCE: Oh, geez, how many ways do we have to measure weight? Wikipedia shows six different ways to measure an ounce. The most common one we use in the United States is the avoirdupois ounce, one 16th of an avoirdupois pound.
POUND: The avoirdupois pound, in turn, is based off of the troy pound, another system entirely. There is a troy 'master' pound, which the avoirdupois system uses, defining an avoirdupois pound as 7000/5760ths of a troy pound. Each state has a copy. In 1959, an international pound came into being; the US adopted it as the new avoirdupois. The international pound is "one part in 10 million smaller than the U.S. pound avoirdupois that it replaced."
GRAM: The weight of one cubic centimeter of water at maximum density.
GALLON: There are several ways to measure a gallon too, but the one we use in the United States is also known as the wine gallon, which in 1758 was figured as eight pounds of wine.
LITER: The volume of one cubic decimeter.
SECOND: Obviously, a day is how long it takes for the Earth to spin around once, and a year is how long it takes the Earth to orbit the sun. You still have to divide that day up, though. The Earth has periods where the length of a day speeds or slows by minute amounts; the earthquake in Chile was one example. Therefore, a second couldn't be based on anything that had anything to do with the Earth's rotation, which was a problem, since the original measurement was one 86,400th of a day. Since 1967, a second has been "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom." Go ahead and try it at home. Maybe some spare caesium 133 atoms will turn up during spring cleaning.
HOUR: Halves of days, divided into 12ths. Not much to say here.
METRIC TIME: Oh yes. Metric time was attempted. 100 metric seconds to a minute, 100 metric minutes to an hour, 10 metric hours to a day, 10 metric days to a week, renamed a 'dekade', 3 dekades to a month.
The metric months, according to the Frenchmen that instituted it, were rhymed by season and descriptive of the corresponding month, with the metric year starting in late September 1793:
Vendémiaire ('grape harvest'), Brumaire ('fog'), Frimare ('frost'), Nivose ('snowy'), Pluviose ('rainy'), Ventose ('windy'), Germinal ('germination'), Floreal ('flower'), Prairial ('pasture'), Messidor ('harvest'), Thermidor ('summer heat'), Fructidor ('fruit').
Or, as the British quickly called them: Wheezy, Sneezy, Freezy, Slippy, Drippy, Nippy, Showery, Flowery, Bowery, Wheaty, Heaty, Sweety.
Oh, yes, and each day of the year got its own name too. Every fifth day would be named for an animal, every 10th day would be named for a tool, every other day would be named for a plant or mineral. Today, what we know as March 11, would be the 21st day of Ventose, Mandrake Day. A sampling of some other days, some of which are just unfortunately named:
Grape Day (September 22)
Donkey Day (October 6)
Hemp Day (October 12)
Plough Day (October 31)
Turkey Day (November 5)
Wax Day (December 1)
Dog Day (December 25)
Lava Day (December 26)
Topsoil Day (December 27)
Manure Day (December 28)
Clay Day (January 1)
Cat Day (January 14)
Zinc Day (January 17)
Axe Day (January 29)
Spinach Day (March 6)
Radish Day (April 8)
Pansy Day (April 17)
Basket of Gold Day (May 7)
Carp Day (May 14)
Scythe Day (May 29)
Pitchfork Day (June 8)
Mule Day (June 23)
Tobacco Day (July 4)
Watering Can Day (July 28)
Basil Day (August 1)
Marshmallow Day (August 3)
Rapeseed Say (August 14)
Puffball Day (August 20)
Bitter Orange Day (September 12)
Pack Basket Day (September 16)
As for the five spare days, days 361-365 (September 17-21)? 'Complimentary Days', celebrating, in order, virtue, talent, labor, convictions and honors, were tacked on to the tail end of the year. Leap years added 'Revolution Day'.
It got laughed right out of existence, and Napoleon banned it at the conclusion of 1805. Which is a hell of a way to celebrate Granite Stone Day.