Concrete Mix Ratio Calculator
Calculate the right cement, sand, gravel, and water proportions for any concrete mix ratio. Enter values for instant results with step-by-step formulas.
Formula
Material Volume = (Parts / Total Parts) × Total Volume
Divide each material's ratio number by the sum of all parts to get its fraction. Multiply that fraction by the total volume in cubic feet (cubic yards × 27). Cement is measured in 94-lb bags (≈1 cu ft each). Sand and gravel are measured in cubic yards. Water is approximately 5 gallons per bag of cement at a 0.45 water-cement ratio.
Worked Examples
Example 1: Driveway Slab — 5 Cubic Yards
Problem: Calculate materials for 5 cubic yards of concrete using a standard 1:2:3 mix ratio.
Solution: Total parts = 1 + 2 + 3 = 6\nCement = (1/6) × 5 × 27 = 22.5 cu ft ≈ 23 bags\nSand = (2/6) × 5 × 27 = 45 cu ft = 1.67 cu yd\nGravel = (3/6) × 5 × 27 = 67.5 cu ft = 2.50 cu yd\nWater = 23 × 5 = 115 gallons
Result: 23 bags cement, 1.67 cu yd sand, 2.50 cu yd gravel, 115 gal water
Example 2: Foundation Footing — 2 Cubic Yards
Problem: Calculate materials for 2 cubic yards of concrete using a 1:2:4 economy mix.
Solution: Total parts = 1 + 2 + 4 = 7\nCement = (1/7) × 2 × 27 = 7.71 cu ft ≈ 8 bags\nSand = (2/7) × 2 × 27 = 15.43 cu ft = 0.57 cu yd\nGravel = (4/7) × 2 × 27 = 30.86 cu ft = 1.14 cu yd
Result: 8 bags cement, 0.57 cu yd sand, 1.14 cu yd gravel
Frequently Asked Questions
What does a concrete mix ratio like 1:2:3 mean?
A concrete mix ratio like 1:2:3 describes the proportional volumes of cement, sand (fine aggregate), and gravel (coarse aggregate). In a 1:2:3 mix, for every 1 part cement, you add 2 parts sand and 3 parts gravel. These ratios are by volume, not weight. The ratio determines the concrete's strength, workability, and cost. Higher cement content (like 1:1:2) produces stronger concrete but costs more. Lower cement content (like 1:3:6) is weaker but more economical for non-structural applications.
Which mix ratio should I use for a driveway or garage floor?
For driveways and garage floors, use a 1:2:3 mix ratio which produces concrete rated at 3,000-4,000 PSI. This is the standard general-purpose mix suitable for most residential applications. If you expect heavy vehicles like RVs or trucks, consider a stronger 1:1.5:3 mix for 4,000-5,000 PSI. The minimum recommended strength for driveways is 3,500 PSI with 5-6% air entrainment in freeze-thaw climates.
How many bags of cement are in a cubic yard of concrete?
For a standard 1:2:3 mix, you need approximately 5-6 bags of Portland cement (94 lbs each) per cubic yard of concrete. The exact number depends on the mix ratio: a 1:2:3 mix uses about 4.5 bags, a 1:2:4 mix uses about 3.9 bags, and a high-strength 1:1:2 mix uses about 6.75 bags per cubic yard. These are approximate figures since actual quantities vary with aggregate moisture content and compaction.
How much water should I add to a concrete mix?
The water-to-cement ratio typically ranges from 0.40 to 0.55 by weight. For each 94-pound bag of cement, use about 5 gallons of water for a workable mix. Too much water weakens concrete significantly — adding just one extra gallon per bag can reduce strength by 25%. The concrete should be workable but not soupy. A proper mix holds its shape when formed but is plastic enough to fill forms and consolidate around rebar.
Can I mix concrete by hand or do I need a mixer?
Hand mixing is feasible for small projects up to about 0.5 cubic yards (roughly 14 bags of 80-lb mix). Use a wheelbarrow or mixing tub and a hoe. For 0.5 to 2 cubic yards, rent a portable mixer (ranging from 3.5 to 9 cubic feet capacity). For anything over 2 cubic yards, order ready-mix delivery — it is more consistent, faster, and often cheaper per yard than buying bags. Hand mixing produces less uniform concrete than machine mixing.
How do I calculate the amount of concrete needed for a project?
Calculate volume in cubic feet (length x width x depth), then divide by 27 to convert to cubic yards. Add 5-10% for waste and spillage. One cubic yard of concrete covers 81 square feet at 4 inches thick.