The first time I needed this information, I literally spent a couple of days searching for a solution that was not going to cost me a fortune in new reference books or computer software. Out of despiration, I posted my need on the Water and Wastwater Dot Com http://www.waterandwastewater.com/ help forum. One of the reqular contributors of this site was kind enough to direct me to the Chemical Engineer's Handbook of which we had a copy of in our Engineering Library. There I found data that allowed me to calculate the volume for any level in the tank I was working with thereby ending the frustration that I experienced while searching for a solution. Said data includes information for ASME dished ends.