Basics

The Combination of Aggregate and Cement
It takes 5 94 lb bags of cement to make a yard of concrete [1]. In other words, a 50kW Solar Concrete plant will make a yard of concrete daily. Or, 10 days to make a slab foundation for Rosebud models of the Seed Eco-Home

Formula

To make 1 yard - To make 1 cubic yard of concrete, you'd need seven 94-pound bags of cement, about 1/2 cubic yard of sand and just over 3/4 cubic yard of gravel. The amount of water you use depends on how wet the sand is.Oct 1, 2009 [2]
10% cement, 75% aggregate, 15% water [3]
150 kg/m3 of cement - with concrete at 4000 lb/cu yd [4] - was sufficient to get about 6000 psi concrete strength [5]. Does this mean abouut 8% of cement?
500 lb per yard of cement in concrete is recommended - read a thesis on it - [6]
Lean or rich: 7-15% cement by volume -

Lean concrete per california codes is 300 lb cement per yard of concrete, and is 700 PSI at 7 days. [7]
Lean is used below foundations - and is 700 psi or 1100 psi [8]

Measures inches of collapse, from 0-12", of a wad of concrete in a cone. 12" means it's complete water. 4" is very stiff.