Mix ratio formula
The 1.52–1.54 dry factor is a common rule of thumb for bulking and voids . It is shown and editable, so you can match the figure your supplier or engineer uses.
Worked example: 1 yd³ at 1 : 2 : 3
- Wet volume: 27 ft³. Dry volume: 27 × 1.54 = 41.58 ft³.
- Parts: 1 + 2 + 3 = 6.
- Cement: 41.58 ÷ 6 = 6.93 ft³, so 7 bags at 94 lb (≈ 1 ft³ each).
- Sand: 41.58 × 2 ÷ 6 = 13.86 ft³ (0.51 yd³).
- Gravel: 41.58 × 3 ÷ 6 = 20.79 ft³ (0.77 yd³).
Common ratios
| Ratio | What articles often say | Cement bags per yd³* |
|---|---|---|
| 1 : 2 : 3 | General slabs, sometimes "~3000 PSI" | 7 |
| 1 : 1.5 : 3 | Driveways, higher cement | 8 |
| 1 : 2 : 4 | Sidewalks, paths, sometimes "~2200 PSI" | 6 |
| 1 : 1 : 2 | Rich mix for small structural items in some articles | 11 |
| 1 : 3 : 6 | Lean fill or blinding | 5 |
*At a 1.54 dry factor and 1 ft³ per 94 lb bag, rounded up. PSI labels are other sites' claims, not a specified strength .
1:2:4 concrete mix calculator
Tap the 1 : 2 : 4 preset above. For one cubic yard you get about 5.94 ft³ of cement (6 bags), 11.88 ft³ of sand, and 23.76 ft³ of gravel. Some guides call this a sidewalk mix. It uses less cement than 1 : 2 : 3, so it is cheaper and generally weaker.
Ratios from other standards
Some mix tables online follow Indian Standard (IS) grades such as M15 or M20, or metric bag sizes like 50 kg. Those are not US bag math and do not map to US PSI. This calculator uses US 94 lb bags by default.
Bagged mix is simpler
Premixed bags already contain cement, sand, and gravel, so you just add water. For small jobs that is usually easier. See the concrete bag calculator. To get the volume first, use the main concrete calculator.
Not a mix design. Water-cement ratio, slump, air entrainment, and strength need a tested design or the product directions.