Concrete Calculator

This concrete slab calculator estimates the concrete volume and bag count for a rectangular slab, including a waste allowance.

Formula notes

volume = length × width × thickness; bags = volume / yield per bag; add waste % on top of the net volume.

Worked examples

1. Example: a 5 m × 4 m slab at 0.1 m thick with 5% waste needs 2.1 m³ of concrete.
2. A 4 m by 3 m slab with a 0.12 m depth requires 1.44 m3 of concrete before adding waste, over-excavation, or delivery rounding.

How to use it

1. Enter the slab length, width, and thickness.
2. Add a waste percentage for spillage and uneven ground.
3. Read the total volume and bag count.

Frequently asked questions

Limits and interpretation

• The page models a rectangular slab and does not include footings, thickenings, voids, slopes, or reinforcement displacement.
• Bag yield and ready-mix order sizes vary by product, moisture, compaction, and supplier rules.

References

• NIST: SI Units