Concrete Mix Ratio Calculator
Work out cement, sand, and aggregate quantities for a classic 1:2:4 nominal concrete mix from the total volume you need to pour.
How this calculator works
A 1:2:4 mix is a nominal concrete mix made of 1 part cement, 2 parts sand, and 4 parts coarse aggregate by volume — 7 parts total. This calculator takes the total volume of concrete you need and splits it into cement, sand, and aggregate volumes using those proportions, then converts the cement volume into standard 94-lb bags.
Because the ratio is fixed, every material’s share is just the total volume divided by 7 and multiplied by its number of parts. The bag conversion uses the common approximation that a 94-lb bag of cement takes up about 1.25 cubic feet loose.
Formula: A 1:2:4 mix has 7 total parts by volume (1 cement + 2 sand + 4 aggregate). Cement volume = total ÷ 7 × 1; sand = total ÷ 7 × 2; aggregate = total ÷ 7 × 4. A 94-lb bag of cement is about 1.25 cubic feet loose, so bags = cement cubic feet ÷ 1.25.
Worked example
27 cubic feet needed (1 cubic yard):
- Total volume: 27 ft³ ÷ 7 = 3.857 ft³ per part
- Cement: 3.857 × 1 ≈ 3.86 ft³
- Sand: 3.857 × 2 ≈ 7.71 ft³
- Aggregate: 3.857 × 4 ≈ 15.43 ft³
- Cement bags (94-lb): 3.86 ÷ 1.25 ≈ 3.09 bags
Notes
1:2:4 is a common nominal mix used for general-purpose footings and slabs, and it lands roughly in the mid-strength range for that kind of work. Where a project calls for higher strength, a richer 1:1.5:3 mix — with proportionally more cement relative to sand and aggregate — is often used instead.
Nominal ratios like this are a practical shortcut for everyday jobs, not a substitute for a tested design mix when strength requirements are strict.
How to use
Enter the total volume of concrete you need in cubic feet. The calculator splits that volume into cement, sand, and aggregate quantities using the 1:2:4 ratio, and converts the cement portion into the number of 94-lb bags to buy.
Nominal mix ratios are a general-purpose guide. For structural work, use a specified design mix or ready-mix concrete rated to the required PSI.
Frequently asked questions
What does a 1:2:4 mix ratio mean?
The numbers are proportions by volume: 1 part cement, 2 parts sand, 4 parts coarse aggregate (gravel or crushed stone). Added together, that's 7 total parts, so each material gets its share of the total volume based on its number of parts out of 7. It's a nominal mix, meaning the proportions are fixed rather than calculated to hit a specific strength.
How much does a bag of cement cover?
A standard 94-lb bag of Portland cement is about 1.25 cubic feet loose. Dividing the cement volume you need by 1.25 tells you how many bags to buy, though you'll typically round up since partial bags still need to be purchased whole.
Is 1:2:4 concrete strong enough for a driveway or footing?
A 1:2:4 nominal mix is commonly used for general-purpose footings, slabs, and similar work and is roughly in the mid-strength range. For structural elements or anything load-bearing beyond typical residential use, check with a local code or engineer, since some projects call for a richer mix or a specified design mix instead.
What's the difference between a nominal mix and a design mix?
A nominal mix like 1:2:4 uses fixed, pre-set proportions that work reasonably well across common uses without lab testing. A design mix is calculated and tested to hit a specific compressive strength (PSI) for a particular project. Nominal mixes are convenient for general work; design mixes are used when strength requirements are strict.
Estimates only. Verify quantities with your supplier before purchasing.