Concrete Calculator
Estimate concrete volume, cubic yards, and full bags.
Estimate concrete
For a rectangular slab. Use the bag's printed cured-volume yield.
Material estimate
Full bags
- Slab volume
- 33.33 cu ft
- Volume with extra
- 36.67 cu ft
- Cubic yards with extra
- 1.36 cu yd
Quantity estimate only; this does not determine structural design or code requirements.
Your entries and results stay in this browser. This tool does not send, save, or add them to the page address.
Estimate concrete for a rectangular slab
Enter the slab length and width in feet, thickness in inches, an extra-material allowance, and the cubic-foot yield printed on one bag. The result shows volume before and after the allowance, cubic yards, and complete bags.
Formula
Slab volume in cubic feet equals length multiplied by width multiplied by thickness divided by 12. Total volume includes the selected extra percentage. Cubic yards equal total cubic feet divided by 27. The bag count divides total cubic feet by bag yield and rounds upward.
Measurements and ordering
Measure the excavated or formed space at several points because real surfaces are rarely perfectly level or square. Bag yield varies by product and bag size. For ready-mix delivery, suppliers may use minimum orders and project-specific ordering increments.
This tool estimates material quantity only. It does not design a slab or determine excavation, subbase, reinforcement, drainage, joints, curing, load capacity, or code compliance. Seek appropriate local or professional guidance for consequential work.
Frequently asked questions
How is concrete volume calculated?
Length and width in feet are multiplied by thickness converted from inches to feet. Extra material is then added using your chosen percentage.
How many cubic feet are in a cubic yard?
One cubic yard contains 27 cubic feet. The calculator divides total cubic feet by 27 to display cubic yards.
What bag yield should I enter?
Use the cured-volume yield printed by the manufacturer for the exact bag size and product. Nominal bag weight alone does not determine volume.
Does this determine the correct slab thickness or concrete specification?
No. Thickness, reinforcement, base preparation, joints, drainage, mix specification, and local requirements depend on the project. Obtain qualified guidance when structural performance or safety is involved.