I've spent much of the last few months learning how to make hay by hand, starting with a scythe. I've gotten good enough that I think I can harvest the bulk of the hay that my goats will need for the winter. It was hard finding an estimate of how much hay goats will eat, but the number I found was 5 lbs/goat/day. At 15 goats for 90 days, that works out to 6750 lbs of hay.
It was even more difficult to find a formula to estimate the weight of a given volume of loose hay. Finally, I found a Canadian site which said that there were 60 kg/m3. That works out to 3.75 lbs/ft3. Assuming that I did all of the calculations correctly, I need 1800 cubic feet of loose hay.
The weather has been dry this week, so I've been cutting hay every day. This will be the first time cutting the entire pasture by myself (last time the goats helped). I think it's quite likely that I'll have enough hay just from this cutting, but there should be another cutting before winter to give me some surplus.