How this calculator works
Convert slab dimensions to cubic feet and cubic yards, then estimate bag counts from a selectable bag yield.
Formula
Volume = length × width × thickness in feet. Apply waste, divide by 27 for cubic yards, or divide cubic feet by bag yield for bag count.
Volume = length × width × thickness in feet. Apply waste, divide by 27 for cubic yards, or divide cubic feet by bag yield for bag count.
Example
A 12 × 10 ft slab at 4 inches thick is about 1.48 cubic yards before waste.
Reliability check
Verify slab thickness at several points and calculate thickened edges, footings or grade beams separately. Bag yield comes from the exact product; structural thickness does not come from this calculator.
How to get a better estimate
- Subgrade depth and form dimensions should be measured, not assumed.
- Bag yield varies by bag size and mix.
- Large pours are usually more practical as ready-mix.
What the result means
The geometric slab volume does not include footings, thickened edges, grade beams or an uneven subgrade. Structural concrete work should follow a qualified design and local requirements.
Reference tables
Compare slab dimensions and thickness with the concrete table, then replace bag yield with the selected mix label.