Concrete mixing ratios are the formula for calculating the correct amount of each ingredient used, including water, cement, sand and aggregate, to produce concrete with the properties desired. A basic concrete ratio is one part cement, two parts sand, and three parts gravel, slowly mixing in water until workable.
Water is the key ingredient, because the water-to-cement ratio is inversely proportional to the concrete's strength properties. Water must be added slowly to the mixture with a slump test performed to determine when the concrete reaches the correct, workable consistency. A slump test consists of filling an inverted Styrofoam cup that has the bottom removed with the mixture. When the cup is removed and the material settles, it should be one-half to three-quarters as tall as the cup for proper workability.