What does it mean?
A mix ratio states proportions of constituents on a stated basis, such as cement, sand and coarse aggregate by volume. The basis must be explicit because ratios by mass and by loose volume are not interchangeable. A nominal proportion is not itself proof of a specified strength, workability or durability. Designed mixes require appropriate specification and quality control.
In practice
A stated 1:2:4 volume ratio describes one part cement, two parts sand and four parts aggregate on that measuring basis. It does not mean seven loose-volume parts will yield seven parts of finished concrete.
Keep in mind
When preparing an estimate, record the specification reference, units and source of each assumption. Separate the net measured quantity from purchase allowances so changes remain easy to trace. Confirm product dimensions, yields and installation requirements with the supplier. Quantities do not establish structural adequacy or material suitability: use the project’s approved design and details, and seek the responsible designer’s clarification where the specification is incomplete.