Concrete Calculator - Slab Volume, Bags & Cost
Calculate concrete for rectangular or round slabs. See cubic meters, bags, waste and costs with the formulas shown.
Dimensions
Prices and bags (optional)
Use the mixed-concrete yield printed on your bag, not its dry weight. Leave blank for volume only.
Enter your supplier's prices. Delivery, labor, reinforcement and taxes are not included unless your quote includes them.
Concrete to order
Enter the yield per bag to estimate how many to buy.
Add a local price to estimate material cost.
Formulas and assumptions
- Rectangle: area = length × width. Circle: area = π × (diameter ÷ 2)². Multiply by the number of identical sections.
- Net volume = area × thickness. Order volume = net volume × (1 + waste ÷ 100). Convert all dimensions to meters first.
- Bags = round up (order volume in liters ÷ mixed yield per bag in liters). Bag cost = whole bags × bag price; ready-mix cost = order volume in m³ × quoted price per m³.
Material estimate only. This tool does not determine slab thickness, concrete strength, reinforcement, foundations or structural safety. Confirm design and supplier yield with a qualified professional.
How to estimate concrete and its cost
- Choose a rectangular or circular slab, enter dimensions, thickness and the number of equal sections. Switch between meters/centimeters and feet/inches if needed.
- Set a waste allowance based on the job. The tool shows geometric volume and the larger order volume separately, so you can see exactly what the allowance adds.
- For bagged mix, enter the manufacturer's mixed yield in liters per bag. Add your local price per bag or per cubic meter of ready-mix to compare material-only costs.
- The formulas appear with the results. Verify the actual thickness, mix specification, delivery minimums and local prices before ordering; this is not a structural design calculator.
Concrete estimate questions
Why not calculate bags from bag weight?
Dry bag mass does not uniquely determine mixed yield. Products vary; use the yield printed in the manufacturer's data sheet or package.
Is waste included in the first volume?
No. Geometric volume is the exact shape; order volume adds your selected waste percentage. Bag count and prices use the order volume.
Does this calculate slab strength?
No. Load, soil, reinforcement, joints, curing and required strength need a project-specific professional design.