film development

I have searched the web but have not found an answer. I use expert tanks in a Jobo ATL. I also develop in trays. I like to make up developers from formulas but have not found a method to determine the correct amount of the active developer which should be used for each sheet of film. Many discussions indicate that you MUST have a sufficient amount of the active developer present but I have found no method of how you determine what that amount is. This appears to a real problem when using dilute developers.

Here is a link to capacity data for Kodak D76. Most manufacturers list these for the various developers on their sites:

http://www.kodak.com/global/en/professional/support/techPubs/j78/j78.jhtml?id=0.1.22.14.18.14.7.14.14&lc=en#004

One way to get at it is to use the same amount of stock no matter what the dilution. If what you're mixing calls for 1:1 dilution for 80 sq.in. and you want to try it at 1:3 you'd still use the same amount of stock. So if 1:1 is 250ml of stock to 250ml of water then 1:3 is 250ml stock to 750ml water. Run your film in the entire liter that you diluted.

If what your recipe calls for is to use the mixture without dilution, to dilute I'd use the same amount again. So if 500ml of developer does your 80 sq.in. and you want to dilute you'd add water to that 500ml and use the entire amount that results.

My rule is to always use plenty of developer. There is nothing to be gained by scrimping, only trouble waiting to happen.