Concrete Calculator
Estimate concrete volume and the number of bags needed for slabs, footings, columns and walls.
How to use this tool
- Choose the shape you're pouring (slab, footing, column, wall).
- Enter dimensions and thickness.
- Pick your bag size (if buying bags) or leave empty for ready-mix.
- Set wastage and optional cost per cubic yard/meter.
- Click Calculate to see volume, bags, cost and a full breakdown.
How it works
Volume = area x thickness. Slab/wall = length x width x thickness; footing = length x width x depth; column = radius² x height. Add wastage, then convert to bags using your bag's yield or to ready-mix units.
Tips
- Measure in the same unit system throughout for accuracy.
- Add 10% for irregular ground or hand-mixing losses.
- For footings, measure from the bottom of the trench, not the top.
Limitations
Assumes a standard bag yield and 0.5 cubic-foot per 60 lb bag. Actual yields vary slightly by mix.
Frequently asked questions
How many bags of concrete do I need for a 4x4 slab?
A 4 ft x 4 ft x 4 in slab is about 0.2 cubic yards. That's roughly 11 x 60 lb bags (or 9 x 80 lb bags). Enter your dimensions to get the exact figure with your bag size.
How do you convert cubic yards to bags?
A 60 lb bag yields about 0.45 cu ft (0.017 cu yd); an 80 lb bag yields about 0.60 cu ft. The calculator divides your volume by the bag size you select.
Should I add wastage?
Yes — 5–10% is standard to cover spillage, uneven subgrades and rounding. The calculator defaults to 10% and lets you change it.
Is this suitable for structural concrete?
It's a material estimate, not engineering. Verify mix design and volumes with an engineer or ready-mix supplier for structural pours.