Rule for ascertaining the weight of hay stacks
Measure the length and breadth of the stack; then take its height from the ground to the eaves, and add to this last one-third of the height from the eaves to the top. Multiply the length by the breadth, and the product by the height, all expressed in feet; divide the amount by 27, to find the cubic yards, which multiply by the number of stones supposed to be in a cubic yard (viz in a stack of new hay, six stones; if the stack has stood a considerable time, eight stones; and if old hay, nine stones), and you have the weight in stones.
For example, suppose a stack to be 60 feet in length, 30 in breadth, 12 in height from the ground to the eaves, and 9 (the third of which is 3) from the eaves to the top; then 60 X 30 X 15 = 27000; 27000 ÷ 27 = 1000; and 1000 X 9 = 9000 stones of old hay.
Samuel Salt Statistics and Calculations essentially necessary to Persons connected with Railways or Canals; containing a variety of information not to be found elsewhere 2nd ed Effingham Wilson, London 1846
You too can possess a copy of this invaluable book, which has much useful information about railways and canals