What is a concrete "mix ratio"
The mix ratio is the proportion of cement, sand and gravel used in the mix — for example, 1:2:3 means 1 part cement to 2 parts sand to 3 parts gravel. The 1:2:3 ratio is one of the most common for standard structural concrete (roughly 20-25 MPa).
How the calculation works
The total volume is split between cement, sand and gravel, proportionally to the mix ratio. Cement volume is converted to 50 kg bags (assuming ~0.033 m³ per bag). Water is estimated using an approximate water/cement ratio of 0.55.
Common mix ratios
| Ratio | Typical use |
|---|---|
| 1:2:3 | Standard structural concrete (beams, slabs, columns) |
| 1:3:3 | Screed, sidewalks |
| 1:2:4 | Light foundations, floors |
Note
For structures requiring a specific compressive strength, consult a structural engineer — the ideal mix depends on the aggregate type, cement used and the structure's purpose.
Frequently asked questions
Does the 1:2:3 ratio work for any application?
It's a common general-purpose ratio for simple structural concrete, but for critical structural elements (foundations, long-span beams) always consult an engineer.
How is the number of cement bags calculated?
The cement volume in the mix is converted to 50 kg bags, using cement's approximate bulk density (~1,500 kg/m³, i.e. ~0.033 m³ per bag).
Is the estimated water amount accurate?
It's a general estimate (water/cement ratio ~0.55) — actual water needed depends on aggregate moisture and should be adjusted on site.
Is this ratio "by volume" or "by weight"?
It's a by-volume ratio, the most common in everyday construction practice — for technical by-weight mix designs, consult the cement manufacturer's dosage guide.