The Concrete Calculator estimates mixed volume for slabs, cylinders or a known area with depth. Combine up to 10 regions, add a material allowance and convert volume to cubic feet, cubic yards and cubic metres. Whole bags use the mixed yield you enter; optional prices add a material budget.
Use it for uniform slabs or complete cylindrical pours. Cylinder mode uses diameter and depth. For a post hole already occupied by a post, supply a separately measured net area: the tool does not infer an annular gap. Measure footprints with square footage, or estimate aggregate with gravel.
US inputs use feet for lengths and diameter, inches for depth, and square feet for known area. Metric inputs use metres, centimetres and square metres respectively. Active dimensions must be positive, at most 1e12. Allowance is 0–100%. Enter the bag’s mixed yield in ft³, litres or m³. Prices are optional, non-negative and use one selected currency label.
Rectangle area = length×width. Circle area = π×(diameter/2)². Base volume = sum of area×depth. Adjusted volume = base×(1+allowance/100). Bags = ceiling(adjusted volume/bag yield). Unit factors: 1 ft = 0.3048 m; 1 in = 0.0254 m; 1 ft³ = 0.028316846592 m³; 1 yd³ = 0.764554857984 m³.
A 12 ft×10 ft slab at 4 in thick has volume 12×10×(4/12)=40 ft³, about 1.481481 yd³ or 1.132674 m³. With no allowance and an illustrative mixed yield of 0.6 ft³ per bag, 40/0.6=66.666667, so buy 67 whole bags. At an example 8 currency units per bag the material cost is 536; this is not a market quote.
Use the product's mixed concrete yield, not bag weight. The example's 0.6 ft³ per bag is illustrative and editable.
Bags are rounded up after the allowance. Bag cost uses whole bags; bulk cost uses the unrounded total volume.
Material estimate only. No structural design, rebar, strength, labor, delivery or taxes. Unit switches convert valid dimensions and bulk-price basis; currency labels do not convert prices.
From project dimensions to mixed volume and whole bags.