Concrete
Concrete Bag Calculator
Enter your project dimensions and see how many 40, 60, or 80 lb bags of concrete mix you need.
Inputs
Live estimate
80 lb bags needed
278
- Area
- 500 sq ft
- Cubic feet
- 166.67
- Cubic yards
- 6.17
- Cubic yards (with waste)
- 6.17
- 40 lb bags
- 556
- 60 lb bags
- 371
- 80 lb bags
- 278
Diagram
Live estimate
- Mathematical quantity
- 278
- Placement contingency
- +5% → 292
- Field conditions
- Not applied
- Adjusted requirement
- 292
- Ordering rule
- Round up to whole bag
- Suggested order
- 292
Small over-excavation, form deflection, and pump / handling loss during placement.
What you actually need in the field, before rounding to a supplier-friendly ordering unit.
Estimator confidence
HighSmall over-excavation, form deflection, and pump / handling loss during placement.
Improve confidence: Increase for pumped placements or complex forms.
Why this behavior applies: Concrete is a rigid, formed material. The only real adjustment is placement contingency — form deflection, small over-excavation, and pump / bucket loss.
- Bag yield vs mix batch quality — Bag yields assume a full, correctly-mixed batch.
- Mix in a wheelbarrow or tub — never straight in the hole for anything structural.
- Wet the sub-grade before placing so it doesn't wick water from the mix.
- For anything over ~15 bags, ready-mix is cheaper and faster.
- Buying the exact theoretical bag count and running short on the last footing.
- Adding too much water and losing strength.
- Trying to pour a slab from bags — ready-mix is a better fit.
Smart tips
- Ordering 5–10% extra is standard on irregular layouts. Running short costs more than the excess.
How it's calculated
Cubic feet = length × width × thickness (in ft).
Cubic feet with waste = cubic feet × (1 + waste %).
Bags = ceil(cubic feet with waste ÷ bag yield). Yields: 40 lb = 0.30 cu ft, 60 lb = 0.45 cu ft, 80 lb = 0.60 cu ft.
Material assumptions
- 40 lb bag yields ≈ 0.30 cu ft.
- 60 lb bag yields ≈ 0.45 cu ft.
- 80 lb bag yields ≈ 0.60 cu ft.
- Bagged mix is easier for small pours; ready-mix wins over ~1 cubic yard.
Frequently asked questions
Related calculators
Related articles
Deeper guidance from the Learn library — sizing, depth, waste, and ordering for this material.
- How Much Concrete Do I Need?Concrete estimating comes down to volume, waste, and delivery format. Here's the math and the decision rule between bags and ready-mix.
- How to Estimate Concrete for a SlabCubic yards = area × thickness ÷ 27. Add 10% waste. Over ~1 cubic yard, switch from bags to ready-mix.
Bag yields are nominal. Confirm with the manufacturer's data sheet for the specific product.