Tallow is rendered cow or mutton fat, but for the sake of argument let’s go with cows here.
How much do cows weigh? Between 1,100kg for a male (bull) and 720kg for a female. So, on average, a cow weighs 910kg.
The body fat content of an average cow is 25 percent. Therefore, the amount of fat in an average cow’s body is 227.5kg.
How many kilograms of this fat is contained in offcuts you could use to make tallow? About 40kg, according to a man at the James Elliott butcher in Islington.
How much tallow is used in one note, according to the Bank of England? “A trace”, which chemically means less than 100 parts per million, or 0.01 percent. A polymer consultant I called confirmed that the tallow present in a given polymer would be a fraction of a single percentage.
New £5 notes weigh 0.7g, therefore there is roughly 0.00007 g of tallow present in one £5 note.
How many fivers are in circulation now, and therefore will be around by May of 2017, when all the old paper ones have been phased out? 329 million notes.
To work out how much tallow will be used in total in all of these fivers, we need to multiply 0.00007g by 329 million, which gives us 23,030g, or 23kg.
And if you get about 40kg of tallow-worthy fat from the average cow, how many cows would you need to make every single £5 note in circulation?
JUST OVER HALF OF ONE COW
http://www.vice.com/en_uk/read/a-very-precise-calculation-of-exactly-how-many-cows-are-being-murdered-for-the-new-fivers