Concrete Mix Ratio Calculator
Calculate how many bags of cement, cubic feet of sand, and cubic feet of gravel you need for any concrete volume and mix ratio.
Understanding Concrete Mix Ratios
Concrete is made from three dry ingredients — cement, sand (fine aggregate), and gravel (coarse aggregate) — plus water. The ratio of these ingredients determines the strength, workability, and durability of the finished concrete. Mix ratios are written as cement : sand : gravel. A 1:2:3 ratio means one part cement to two parts sand to three parts gravel, by volume.
Mix Ratio Strength Guide
The standard 1:2:3 mix (sometimes called “nominal mix”) produces concrete with a compressive strength of approximately 3,000 PSI (20 MPa) after 28 days. This is suitable for most residential applications: driveways, patios, pathways, and fence footings. A stronger 1:1.5:2.5 mix produces approximately 4,000 PSI (25–30 MPa) and is used for garage floors, structural slabs, and load-bearing applications. The 1:1:2 foundation mix produces approximately 5,000 PSI (35 MPa) and is specified for footings, foundations, and high-stress structural elements. Always check your local building code for required concrete strength in structural applications.
Water-to-Cement Ratio
Water is not included in dry ingredient ratios but is critical to strength. A lower water-to-cement ratio produces stronger, more durable concrete. A typical ratio is 0.45–0.55 kg of water per kg of cement. Adding too much water weakens the concrete significantly — resist the urge to make it more workable by adding water. Use plasticizers if workability is needed without sacrificing strength.
Cement Bags
In the United States, cement is sold in 94-lb bags (one cubic foot per bag when dry). One 94-lb bag, combined with the correct amounts of sand and gravel, produces approximately 0.67 cubic feet of finished concrete. Always buy 10% extra to account for waste, spillage, and mixing residue.
Curing
Proper curing is as important as the mix ratio. Keep fresh concrete moist for at least 7 days by covering with plastic sheeting or burlap and wetting regularly. Concrete reaches 70% of its 28-day strength in the first 7 days; the remaining 30% develops over weeks to months. Do not apply loads to fresh concrete until it has cured at least 7 days for foot traffic, 28 days for vehicle traffic.