The weight of a bail of hay depends on how big the bail is. On average a large bail is 180 by 180 centimetres and can weigh up to 1000 kilograms. It also depends on the machine that does the bailing.
1 Additional Answer
The weight of a bale of hay differs depending on the size and the moistness content. A bale of hay that can be credited at feed stores weighs between 60 and 130 pounds while a large one weighs between 1500 and 2000 pounds.