Concrete Mix Calculator
Bags of concrete mix for any slab, footing, or column
What is concrete mix calculator?
A concrete mix calculator sizes the number of bags of premixed concrete you need to buy. “Concrete mix” is the bagged product at every hardware store — portland cement plus sand plus gravel plus admixtures, all dry-blended in the right ratio. Add water and you have concrete. Yield is 0.60 ft³ per 80-lb bag, identical across Quikrete, Sakrete, and store-brand variants.
Concrete mix vs cement — the terminology trap. People use the words interchangeably, but they’re different products. Cement (portland cement) is just the binder powder, sold in 94-lb bags or bulk. Concrete mix is a premixed product — cement + sand + gravel — ready to mix with water. If you bought a bag labeled “cement,” it has no aggregate, and pouring it as-is gives you a brittle, useless lump. The Cement Calculator covers raw cement; this tool covers premixed mix.
Why bagged premixed exists. For small pours, mixing your own from raw cement, sand, and gravel is a hassle — measuring ratios, sourcing aggregate, hauling materials. The premixed bag is convenience, not strength. Past 1 cubic yard, ready-mix from a concrete plant is cheaper than bags. Below that, the bag premium is worth it.
The math is bag-yield-driven, not weight-driven. A common mistake is dividing project weight by bag weight: “I need 4,000 lb of concrete, so 50 of 80-lb bags.” Wrong. The right math is volume ÷ bag yield: 1 cu yd = 27 ft³ ÷ 0.60 ft³ per bag = 45 bags. The 80 lb of dry mix becomes ~100 lb of wet concrete after water (~6 pints per bag), so weight-based math underestimates by 20%.
Mixing tips. One bag at a time in a wheelbarrow keeps your water ratio honest. Past 3-4 bags, rent a small mixer — uniform mix, no cold joints, faster cycle time.
When to use a concrete mix calculator
- Hardware store premixed bags — Quikrete, Sakrete, and store-brand bagged concrete are all 'concrete mix' — premixed portland cement, sand, and gravel. Just add water. The yield is 0.60 ft³ per 80-lb bag.
- Compare to custom-mix — If you're mixing portland + sand + gravel from scratch, you skip the bag premium. For pours over a few yards, custom-mix or ready-mix is cheaper. This calculator sizes the premixed alternative.
- Repair and patch projects — Premixed concrete mix is the right product for anything under 1 cubic yard — repairs, patches, post-setting, and small slabs. Above that, switch to ready-mix.
How to use the Concrete Mix Calculator
- Confirm you need 'concrete mix' not 'cement' — Concrete mix = portland cement + sand + gravel + admixtures, ready to mix with water. Cement (portland cement) is just the binder. They're sold separately and are not interchangeable.
- Pick your shape and dimensions — Slab/Pad for flat pours, Footing for rectangular footings, Column for sonotubes. The calculator handles unit conversion (inches to feet).
- Pick your bag size — 80-lb bags = 0.6 ft³ each. 60-lb = 0.45 ft³. 40-lb = 0.3 ft³. Yields are identical across Quikrete, Sakrete, and store brands.
- Buy 1-2 extra bags — Premixed bags are returnable unopened. Running short mid-pour is a disaster. The 10% waste factor handles most realistic scenarios; rough subgrade pushes it to 15%.
Worked examples
Patio: 8 × 10 ft × 4 in
Input: Slab tab: 8 ft × 10 ft × 4 in
Output: 0.99 cu yd / 45 of 80-lb bagsFooting: 20 ft × 16 in × 12 in
Input: Footing tab: 20 ft × 16 in × 12 in
Output: 0.99 cu yd / 45 of 80-lb bagsSonotube: 8 in dia × 4 ft
Input: Column tab: 8 in dia × 4 ft
Output: 0.05 cu yd / 3 of 80-lb bags