Concrete Mix Ratio Calculator

Enter the volume of finished concrete you need, then pick a mix ratio or strength class such as 1:2:3 for about 3000 psi. The calculator multiplies your volume by a 1.54 dry-volume factor, splits that dry volume by the ratio, and reports cement (as 94 lb bags), sand, gravel, and water. You can switch the volume unit between cubic feet, cubic yards, and cubic meters, or enter a custom ratio.

The ratio is cement to sand to gravel by volume, and a higher cement share gives stronger concrete. A 1:2:3 mix reaches about 3000 psi and suits most slabs, footings, and driveways, while 1:1.5:3 (about 3500 psi) and 1:1:2 (about 4500 psi) are used for structural work. Leaner mixes like 1:2:4 (2500 psi) or 1:3:6 (1500 psi) work for paths and non-structural fill. Strength values are approximate and depend on materials, curing, and the water-cement ratio.

Dry cement, sand, and gravel hold air voids that disappear once the materials are combined and compacted. To produce a given volume of finished concrete you batch about 1.54 times that volume in loose dry materials, since the cement and water fill the gaps between the aggregate. This calculator applies that 1.54 bulking factor before splitting the materials by your mix ratio.

The water-cement ratio is the weight of water divided by the weight of cement. Lower ratios near 0.4 give stronger, more durable concrete but stiffer mixes that are harder to place, while ratios near 0.6 are easier to work but weaker. The calculator sets water weight as the ratio times the cement weight, then converts to gallons at 8.34 lb per gallon. Add water gradually, because aggregate moisture and weather change how much you actually need.

The calculator assumes one 94 lb bag of Portland cement fills about one cubic foot, so the bag count equals the cement volume in cubic feet, rounded up. For example, 27 cubic feet of 1:2:3 concrete needs about 6.93 cubic feet of cement, which rounds up to 7 bags. If you would rather buy premixed bags than separate cement, sand, and gravel, use a concrete bag calculator instead.

These figures are planning estimates, not a substitute for a tested mix design. Weights use loose bulk densities (cement 94 lb, sand 100 lb, and gravel 105 lb per cubic foot) that vary with moisture and material source, and the strength classes are approximate. Order about 5 to 10 percent extra to cover spillage and uneven ground, and follow the supplier or engineer specifications for structural pours.