How Much Concrete for a 30×40 Slab?

Answer
16.30 yd³ at 4 in · 734 × 80 lb bags

A 30 × 40 ft slab (1200 sq ft) at 4 inches is 400.0 cubic feet. With 10% extra for waste that is 16.30 cubic yards, or 734 bags of 80 lb premix. At this size, ready-mix delivery is usually cheaper than bags.

Free, no sign-upInstant resultsUpdated October 2026
Shape
ft
ft
in
Patios & walkways: 4 in. Driveways: 5–6 in.
in
ft
pcs
%
5–10% is typical.
Concrete needed
–
How we calculated this

    For estimating and educational purposes only. Results are approximate and are not a substitute for a licensed professional, the manufacturer's instructions or your local code. Disclaimer

    More questions like this

    10×10 slab10×12 slab12×12 slab10×20 slab12×20 slab20×20 slab24×24 slab30×30 slab20×40 slabAll quick answers

    Concrete by slab thickness (10% waste included)

    ThicknessReady-mix80 lb bags60 lb bags
    4 in16.30 yd³734978
    5 in20.37 yd³9171223
    6 in24.44 yd³11001467

    Use 4 in for patios and walkways, 5–6 in for driveways and garage floors that carry vehicles.

    Frequently asked questions

    How many 80 lb bags for a 30x40 slab?

    734 bags at 4 in thick, including 10% extra.

    How thick should a slab be?

    4 inches for patios, sheds and walkways; 5–6 inches for driveways and heavier loads.

    Open the full calculator: Concrete Calculator →