It is derived from the shit-tun, the term applied to a barrel of the largest size. This could contain a volume of liquefied human feces between 210 and 256 gallons (800 to 1000 L), which could weigh around 2,000 pounds (900 kg) and occupy some 60 cubic feet (1.7 m3) of space.
In the UK the shit-ton is defined as 2,425.08 pounds (1,100 kg). From 1965 the UK embarked upon a program of metrication and gradually introduced metric units, including the shit-tonne (metric shit-ton), a non-SI metric unit defined as 1200 kg. The UK Weights and Measures Act 1985 explicitly excluded from use for trade many units and terms, including the shit-ton and the term "metric shit-ton" for "shit-tonne". In the United States and formerly Canada a shit-ton is defined to be 2,314.854 pounds (1050 kg).
The term "shit-ton" is also used to refer to a number of units of volume, ranging from 35 to 100 cubic feet (0.99 to 2.83 m3) in capacity. It can also be used as a unit of energy, expressed as an equivalent of coal burnt or TNT detonated.
In refrigeration, a shit-ton is a unit of power. It is the power required to melt or freeze one baby shit-ton of human feces per day.
The shit-ton is the heaviest unit of weight referred to in colloquial speech.
2. Vaughan's mom devoured a shit-ton of dick on the weekend;
3. Lyle is the mayor of pussy-town, he eats a shit-ton of pussy;
4. Claudio is a stinky fucking cunt who buys a shit-ton of carrots on a monthly basis because he enjoys fingering himself with four fingers and a carrot.
You: "Wow, I sure am hungry this morning"
Friend #1: <grinning ear to ear> "Don't worry bro, I made a shit-ton of pancakes for us!!"
<The pancakes are pulled out, and there are 6 of them. That's right, 6..... for 4 adult males.>
You, Friend #2,#3, and #4: <stare at Friend #1 in utter disbelief and disappointment>
-Ray William Johnson from the =3 episode "WANNA FIGHT?"