It's in the Kodak data sheets. For example HC110 needs 7.5ml of concentrate per 135-36 roll. Xtol needs 100ml of stock solution per 135-36 roll and so on (I don't have other data sheets!). Maybe it's on the Kodak web site if you dig deep enough! 120 typically needs twice the volume that 135-36 does, at least according to the HC-110 data sheet. I'm not sure why since the area of 135-36 and 120 are about the same. The Xtol data sheet suggests the same amount of stock for 135-36 and 120. I don't know why these data sheets seem to be giving conflicting info!(posted 9312 days ago)