Of course, even people like me who have never made concrete in a mixer know that it's not an exact science when it comes to quantities of materials. But, it does help to have some inkling of what's in the ballpark when starting out, just to get a rough picture of things. Anyway, as to this 120L mixer, the instruction booklet says this: "Typical maximum quantities include 2 gallons of water, 3 shovels of cement, 15 shovels of aggregate rock using a size 3 shovel." I'm just saying, that the manufacturer gives some input on quantities. Mixer made in China, maybe that's why gallons referenced.