I worked as a field reporter for the local county ASCS office back in the 80's. I was in almost every bin in the county then, plus some in neighboring counties. The formula we used for cones was the diameter squared times .262 times the height of the cone, giving cubic feet which we then converted to bushels. Sometimes we had to do some "mental pushing" if the grain was piled unevenly. Sometimes the height of the cone had to be estimated. We also used the same formula for inverted cones where grain had been drawn out of a bin, subtracting the volume instead of adding it.
One of my biggest challenges was from a farmer who moved reserve corn from a bin on one farm to a quonset on another farm. Enroute, he took it all to town and weighed it before piling it in the quonset. I needed to be sure he had enough grain in the quonset to cover his reserve contract. He knew how much corn he'd weighed and put in there and wanted to see how close I came. It took more than one trip to the quonset to get measurements. When I was done I came within about a hundred bushels of what he said he'd put in.
