Calculate concrete volume for a rectangular pour or a round column or footing, in cubic yards and cubic meters, with a waste factor applied.
V (ft³) = length × width × thickness → ÷ 27 = yd³
For slabs, footings, and walls use length × width × thickness. For columns and sonotubes, volume is π × radius² × depth.
One cubic yard is 27 cubic feet; one cubic meter is about 1.308 cubic yards.
The reason this calculator asks about shape is that different pours use genuinely different geometry. A slab, footing, or wall is a rectangular prism: length times width times thickness. A column, pier, or Sonotube is a cylinder: pi times the radius squared, times the height. Using the wrong one is the most common source of large errors — treating a round column as a rectangle, or vice versa, throws the volume off by more than 20%.
For complex pours, break the structure into simple shapes, calculate each, and add them. A slab with a thickened edge is a thin rectangle plus a deeper perimeter beam. A pier with a belled base is a cylinder plus a frustum. Estimating each piece separately and summing is always more accurate than trying to average.
Footings are notorious for using more concrete than the nominal calculation suggests, and the reason is the trench. Hand-dug and even machine-dug trenches rarely have perfectly vertical walls or a flat, level bottom. Soil sloughs in, the depth wanders, and every bit of over-excavation gets filled with concrete you pay for.
This is why many contractors carry 15% waste on footings rather than the 10% they'd use on a formed slab. If your trench bottom is soft or uneven, or you've over-dug in spots, lean toward the higher figure. It's far cheaper to have a little extra concrete than to stop a footing pour halfway and create a cold joint in a structural element.
Suppose you have continuous footings around a 20 x 30 ft addition: the perimeter is 2 x (20 + 30) = 100 linear feet. If each footing is 16 inches wide and 8 inches deep, that's 1.333 ft x 0.667 ft = 0.889 square feet of cross-section, times 100 ft = 88.9 cubic feet, or 3.29 cubic yards.
Add 10% for the trench bottom never being perfectly flat and you would order about 3.6 cubic yards. Footings are notorious for absorbing extra concrete because the soil sidewalls slough and the trench depth varies — some contractors carry 15% here rather than 10%.
Volumes are exact geometry. The 10% default waste covers spillage and over-pour per ACI/RSMeans guidance.
Multiply length × width × thickness in feet to get cubic feet, then divide by 27.
Break the shape into rectangles and cylinders, calculate each volume separately, and add them together. This split-and-sum method handles almost any pour more accurately than trying to estimate the whole thing at once.
Exactly 27 — a cubic yard is 3 feet by 3 feet by 3 feet. Ready-mix is sold per cubic yard, so this conversion comes up constantly.
Cement is the gray powder that acts as the binder. Concrete is the finished material: cement plus sand, aggregate (stone), and water. You pour concrete, not cement.