The amount of faeces that a broiler produces is dependend on the amount of feed that it eats, on the composition of the feed and the feed conversion, and on the amount of water in the faeces. On top of that, also the amount of litter that is used as bedding material is a factor, as it will add to the layer of litter. Not all of that initial litter and manure will be found at the end of the cycle, as bacteria will composte part of the litter layer into Carbon Dioxide, water, Ammonia and other gases, with metabolic heat as a by-product.
To be able to estimate the amount of manure that a broiler produces, a rule of thumb is that the amount of feed intake is equal to the amount of manure produced when the manure has a water content of 80%*. A quick calculation will show that the amount of manure that is produced in a cycle is highly dependend on the water content of that manure.
If a broiler eats 1000 g of feed, we can estimate that the amount of manure is 1000 g as well, if that manure has a dry matter percentage of 20, and a water content of 80%. This means that 1000 g of manure will contain 200 g of dry matter and 800 g of water. If the water content will be 0%, only dry matter will remain and the total amount of manure will be only 200 g. If the water content is 50%, it means that 50% of the manure is dry matter and 50% is water. If the dry matter is still 200 g, there will be 200 g of water in the manure as well (50/50) and the total amount of manure will be 400 g instead of the initial 1000 g.
The factor composting of the litter is dependend on a lot of factors as water content, caking (oxygen supply) feed formulation etc and is difficult to estimate, but it is clear that the water content will have a major effect on the volume.
* Source: Handboek voor de Pluimveehouderij 1988