How to calculate it
Volume equals length × width × slab thickness using consistent units. Add a planning allowance, then divide by the concrete mix bag yield printed on the package.
Worked example
A 10 × 8 ft slab at 4 in thick is 26.67 cu ft, or about 0.99 cubic yards before allowance. At 0.6 cu ft of finished concrete per bag, that is 45 bags before extra allowance.
Before you order
- For large slabs, ready-mix delivery may be easier than hand-mixing many bags.
- Always use the finished yield printed on the exact product you plan to buy.
- Do not use this estimator as structural engineering or as approval for local frost depth, slope and reinforcement.
This is a planning estimate using simple geometry and your inputs. It does not account for every site condition, local construction code, labour price or product requirement. Verify any critical dimensions or structural details with a qualified professional.
Frequently asked questions
What is bag yield?
It is the volume of finished concrete a bag makes after proper mixing. It varies by mix and weight; look on your bag.
Can this size footings or foundations?
No. Structural work requires design, local code checks and potentially permits.
Is cubic yard volume the same as cubic foot volume?
No. One cubic yard contains 27 cubic feet.
Sources & assumptions
Geometry-based estimate. Your product specifications and supplier instructions take priority.
Calculator formulas and explanations prepared for RenovationBinder, 2026-10-15.