An auditor with a large food company has asked about procedures for feed inventory counts. The general process is to determine the volume of each feed ingredient stored and to then multiply it by the stored density to yield a weight of feed in storage. The University of Wisconsin-Madison and USDA have jointly created several excellent spreadsheet models for deriving feed inventory counts. Click here to access their pile density calculation spreadsheet, and here to access their documentation of the spreadsheet. This is an extremely detailed calculation, going well beyond the usual cubic dimension inputs to also require the average dry matter content, packing layer thickness, packing tractor weight, and tractor packing time.
Also, click here to access their spreadsheet for determining the average grain density in a bunker silo, and here for their documentation of the spreadsheet. This model uses as inputs most of the information just noted for the pile density calculation, as well as the bunker silo dimensions.
In addition, click here to access a spreadsheet for estimating the average density of forage in a storage unit based on the weight of the feed removed and the calculated volume of that feed. Click here for the related spreadsheet and procedure documentation.
Additional feed inventory tables have been compiled by the University of Wisconsin for determining the storage capacity of different types of structures, which can be accessed here. The tables include dry matter capacities of upright silos, how to calculate the capacity of a partially fed silo, the cubic storage capability of circular storage structures, and the storage capacity of various sizes of silage bags.