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Concrete Calculator

Work out how much concrete a slab, patio, or footing needs, in cubic yards for a truck order or bags for a small job.

Your numbers

ft
ft
in
%

Concrete needed

1.63 cubic yards

80 lb bags
74
Cubic feet
44
Cubic meters
1.25
Show the working
  1. Volume with 10% extra = 44 ft³
  2. Cubic yards = 44 ÷ 27 = 1.63
  3. Bags = 44 ÷ 0.6 ft³ per bag, rounded up = 74

Results are estimates for planning. Check important figures with a qualified professional.

Quick answer

The Concrete Calculator shows cubic yards of concrete and premix bags for a slab, footing, or patio. How it works: Volume = length × width × thickness; Cubic yards = cubic feet ÷ 27. For example, with length of 12 ft, width of 10 ft, and depth of 4 in, the concrete needed is 1.63 cubic yards.

How to use the Concrete Calculator

  1. Enter length.
  2. Enter width.
  3. Enter depth.
  4. Enter extra for waste. Adds a margin for cuts, spills, and uneven ground.
  5. Choose bag size.
  6. Read concrete needed and the breakdown. Use Share to send the exact numbers, or Print to save a PDF.

How it's calculated

  • Volume = length × width × thickness
  • Cubic yards = cubic feet ÷ 27
  • Bags = cubic feet ÷ bag yield (80 lb ≈ 0.60 ft³)

Worked example

With length of 12 ft, width of 10 ft, depth of 4 in, extra for waste of 10 %, and bag size of 80 lb bag (0.60 ft³):

Concrete needed: 1.63 cubic yards. 80 lb bags: 74.

Questions people ask

How thick should a slab be?

4 inches is common for patios and walkways. Driveways are often 4 to 6 inches. Check local code for your project.

Bags or a truck?

Bags suit small jobs. Above about 1 cubic yard, ready-mix delivery is usually easier and often cheaper.