I'm not very good with litres but hopefully this will help.
This 14 litre bag of carefresh (size wise) fits at least 3 x into a 4kg bag of fitch first. There is also more of the fitch first bag left at the top - so rough estimate is more than 42 litres in a 4kg bag as they roughly look about the same compressed state. so 20kg could be a bit less or a bit more than 210litres as this is all just rough guess work
Bedding forum.jpg
Bedding forum 2.jpg
Bedding a forum.jpg
This pic shows the 4kg bag of fitch first with the carefresh 14lt in front of it, and an 85 litre of megazorb behind it and a bag of aubiose hemp (20kg) bedding at the back
Bedding forum 3.jpg