Concrete calculator

Pick a slab, a footing strip or round piers. You get cubic yards, the ready-mix order rounded up to a quarter yard with your waste allowance, and the bag count for 40, 60 or 80 lb mix. Nothing leaves your browser.


  

Do the whole house: footing, stem wall, slab, rebar and forms in one takeoff

How it is counted

  1. Volume. Area times thickness, converted from cubic inches: 1,728 to a cubic foot, 27 cubic feet to a cubic yard. A pier is a cylinder.
  2. Waste. Your percentage is added, then the order is rounded up to the next quarter yard, the way plants sell it.
  3. Bags. Volume with waste divided by the label yield of the bag, rounded up.

Questions

How many cubic yards of concrete for a 12 x 12 slab 4 inches thick?

A 12 x 12 ft slab 4 in thick is 48 cu ft, which is 1.78 cu yd. With 10% waste that is 1.96, so order 2 cu yd of ready-mix, or about 88 bags of 80 lb mix at 0.6 cu ft each.

How many 80 lb bags of concrete make a cubic yard?

A cubic yard is 27 cu ft and an 80 lb bag yields about 0.6 cu ft, so 45 bags before waste, 50 with 10% waste. Past about a yard, ready-mix is usually the easier order.

Why add 10% to a concrete order?

Subgrade is rarely dead flat, forms bow a little and some mix is left in the truck and the wheelbarrow. Running short mid-pour leaves a cold joint, so most people over-order slightly. The percentage is yours to change.

Is there a minimum order for ready-mix concrete?

Many plants charge a short-load fee below roughly 3 to 4 cu yd, and the figure varies by plant, so call yours. For one or two yards, compare that fee against bagged mix.