Heston? As in the baler? If it is a hardcore baler then I think you'll find that all Heston balers are variable, so it would depend on the size set. You need to find out the weight of the bale really, to be able to make a good comparable. For example, we use a New Holland round baler and it makes bales of 1,800lbs and that is what we have our baler set at as we want huge bales! If we were making selling bales then we would likely set the baler at around 800lbs, so you would have to ask the farmer to be sure.
As Tia says Hesston is actually a make of baler not strictly speaking a type but farmers love to confuse you! The larg bales are quads or mini quads.
It's all dependant on weight so hopefully your farmer should be able to tell you the weight of the bales.
For hay we work on a small square bale being between 18-25kg.
Mini hesston hay 250kg or 10- 12 small bales
A quad about 330 -340kg or 15 - 17 small bales
4 x 4 round bales about 10 small bales or roughly 200kg.
But that varies with the type of baler used so if you can get a idea of the weight before you buy it'll help you work it out.
