Concrete bag calculator
Sometimes you already trust the yardage — a contractor texted “1.5 yards” or you calculated the slab yesterday — and you only need bags. This page starts from volume (cu ft or yd³) or from simple L×W×thickness, then divides by the yield printed on common bag sizes. Round up. Partial bags still mean a full bag at the register, and running out mid-pour is worse than owning one leftover for fence posts next month.
Estimate only — not a contractor bid. Confirm bag yields and local codes before you pour or order.
When to use
Fence posts and small pads; comparing 60 lb vs 80 lb aisle prices; converting a ready-mix quote you declined into a bag plan.
When not to
Do not use bag math alone for a driveway-sized pour unless you enjoy mixing all day. For shape-first estimating, start at the concrete calculator.
Assumptions
Default yields: 40 lb → 0.30 cu ft, 60 lb → 0.45 cu ft, 80 lb → 0.60 cu ft (editable if your bag says otherwise). Waste default 10%. Quikrete / Sakrete style bagged concrete — not mortar, not thinset.
Worked examples
Example 1
0.5 yd³ needed, 10% waste, 80 lb bags
→ 0.55 yd³ → 14.85 cu ft → 25 bags at 0.60 cu ft
Example 2
8 post holes totaling 4.0 cu ft net, 15% waste, 60 lb bags
→ 4.6 cu ft → 11 bags at 0.45 cu ft
Premix post-mix bags sometimes list holes-per-bag — prefer the bag’s own chart when it exists.
How it calculates
Start from yards (or a quick slab), apply waste, divide by bag yield, and round up.
- Enter cubic yards you already trust — or switch to slab dimensions.
- Pick 40 / 60 / 80 lb and set waste.
- Buy the rounded-up bag count; check the yield on the bag you load.
order_cu_ft = volume_cu_ft × (1 + waste) bags = ceil(order_cu_ft / yield_per_bag) If input is yd³: volume_cu_ft = yd³ × 27
Common traps
- Mortar and concrete bags are not interchangeable.
- High-strength or crack-resistant mixes can have different yields — read the back.
- Water is not in the bag count. Have a hose plan before you open twenty bags.
Next tool
Shape → yards first: concrete calculator.
Plain-language shopping question: how much concrete.
FAQ
About 45 at 0.60 cu ft each — verify yield.
Related
Estimate only — not a contractor bid or engineered takeoff. Confirm bag yields and local codes before you pour or order.