How do I convert cubic feet to cubic yards of concrete?

Divide cubic feet by 27, because one cubic yard contains 27 cubic feet (3 ft × 3 ft × 3 ft). For example, 81 ft³ ÷ 27 = 3 cubic yards, and 5.5 ft³ ÷ 27 = 0.20 yd³. The full slab formula is cubic yards = (length × width × depth, all in feet) ÷ 27. Always convert to cubic yards before calling a ready-mix supplier, since US batch plants price and deliver by the yard.

Cubic yards vs cubic feet — which one do I order in?

Order in cubic yards if you are buying ready-mix from a truck (the US standard), and think in cubic feet only when buying bags. A 60 lb bag yields about 0.45 ft³ and an 80 lb bag about 0.60 ft³, so bag counts come from the cubic-foot total, while truck orders come from the cubic-yard total. One cubic yard = 27 cubic feet = 0.765 cubic meters, so keep both numbers handy when comparing bagged vs delivered concrete.

How do I add the volume of several different shapes together?

Calculate each shape in cubic feet using its own formula — rectangular as L × W × D, cylindrical as π × r² × height — then add all the cubic-foot results together before converting to cubic yards. Do not divide each shape by 27 separately and round in between, because the rounding errors compound. Sum the raw cubic feet first, divide the grand total by 27 once, then apply your waste factor. This is how you combine, for example, a slab plus the column footings under it into one ready-mix order.

How do I convert inches of thickness to feet for the volume formula?

Divide the thickness in inches by 12, because there are 12 inches in a foot. A 4-inch slab is 4 ÷ 12 = 0.333 ft, a 6-inch slab is 0.5 ft, and an 8-inch slab is 0.667 ft. Forgetting this step is the most common volume mistake — entering "4" instead of "0.333" for a 4-inch slab overstates the order by 12 times. The calculator above handles the inch-to-foot conversion automatically when you select inches as the depth unit.

How much extra concrete should I over-order?

Add 10% to your calculated volume as a standard waste factor for slabs and footings. Bump it to 15% for footings poured against rough, hand-dug earth or over-excavated subgrade, where the concrete fills voids you cannot measure. For very large flatwork on a well-prepared, screeded base you can drop to 5%. The cost of a little surplus is far smaller than the cost of running short mid-pour and creating a cold joint, which is a permanent weak plane in the finished concrete.

When should I use this general volume tool instead of a shape-specific calculator?

Use this general volume calculator when a project mixes shapes — a slab with round pier footings, a wall with a stepped base, or several pads of different sizes — and you want one combined cubic-yard total. Reach for a shape-specific tool when it adds inputs this one does not, such as bag-size options, rebar layout, or cost per yard. For a plain rectangular pour the dedicated slab calculator is faster, and for round columns the cylinder calculator handles diameter and count directly.

Does concrete density change the cubic-yard result?

No. Volume depends only on the dimensions of the space you are filling, so density (145 lb/ft³ for normal-weight concrete) does not affect the cubic-yard figure at all. Density only matters when you convert that volume into a weight — for example, to check truck axle limits or estimate dead load. To get the weight of a pour, multiply the volume in cubic feet by 145 lb/ft³, or use a dedicated weight calculator.

Concrete Volume Calculator — Cubic Yards, Feet & Meters

What Is a Concrete Volume Calculation?

A concrete volume calculation finds the three-dimensional space a pour must fill, expressed in cubic feet (ft³), cubic yards (yd³), or cubic meters (m³). It is pure geometry — length, width, and depth, or radius and height — independent of mix strength, density, or cost. Getting the raw volume right is the foundation every other number depends on: bag counts come from cubic feet, ready-mix orders come from cubic yards, and weight comes from multiplying volume by density. This calculator is a general-purpose volume engine: enter any rectangular or cylindrical shape and read the answer in all three units at once.

The one conversion that governs US concrete ordering is ÷ 27: there are 27 cubic feet in a cubic yard (3 × 3 × 3). Because ready-mix is sold by the yard, almost every job ends with that single division. Metric users multiply cubic feet by 0.0283 to reach cubic meters instead. Keep all dimensions in the same unit before you multiply — the most common mistake is leaving slab thickness in inches.

Concrete Volume Formulas for Every Shape

Rectangular Volume — Slabs, Walls, Pads, Footings

Volume (ft³) = Length (ft) × Width (ft) × Depth (ft). Convert any thickness given in inches to feet by dividing by 12 (a 4-inch slab is 0.333 ft). This same formula covers slabs, foundation walls, equipment pads, and straight strip footings — only the proportions change. For a dedicated rectangular-slab tool with bag and cost outputs, use the concrete slab calculator.

Cylindrical Volume — Columns, Sonotubes, Post Holes

Volume (ft³) = π × (Diameter ÷ 2)² × Height (ft). Convert the diameter from inches to feet, halve it for the radius, square it, then multiply by π (3.1416) and the height. A round column holds about 0.79 ft³ per foot of depth at a 12-inch diameter. The concrete cylinder calculator handles diameter, depth, and pier count directly.

Footing Volume — Continuous and Stepped

A footing is just a long rectangular prism: Length × Width × Depth. For a continuous perimeter footing, the length is the total run around the building. Stepped footings on a slope are summed segment by segment. The concrete footing calculator adds rebar and stepping logic on top of this base formula.

Irregular and L-Shaped Areas

Break any irregular footprint into rectangles and triangles you can measure, find the area of each, add the areas, then multiply the total area by the depth. An L-shape is two rectangles; a chamfered corner is a rectangle minus a triangle. Compute every sub-shape in cubic feet and total them before the final ÷ 27.

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Concrete Unit Conversions

Concrete is sold by the cubic yard in the United States and the cubic meter elsewhere. Use these conversions when reconciling plans, supplier quotes, and bag yields:

1 cubic yard = 27 cubic feet (the core ÷ 27 rule)
1 cubic yard = 0.765 cubic meters
1 cubic meter = 1.308 cubic yards = 35.315 cubic feet
1 cubic foot = 0.037 cubic yards
Inches to feet: divide by 12 (4 in = 0.333 ft, 6 in = 0.5 ft)
Bag yield: 60 lb ≈ 0.45 ft³, 80 lb ≈ 0.60 ft³

How to Add Multiple Shapes Into One Order

Real pours rarely fit one shape. A garage might be a slab plus four round pier footings; a porch is a slab plus steps. The correct method is to compute each piece in cubic feet, add all the cubic-foot subtotals, and only then divide the grand total by 27. Converting and rounding each shape to cubic yards before adding compounds the rounding error and can throw the order off by a fraction of a yard — enough to matter on a small job.

Slab: 20 ft × 20 ft × 0.333 ft = 133.2 ft³
Four 12-inch piers, 3 ft deep: 4 × (π × 0.5² × 3) = 9.42 ft³
Subtotal: 133.2 + 9.42 = 142.6 ft³
÷ 27 = 5.28 cubic yards; with 10% waste, order 5.8 yd³

For the yard-and-bag side of ordering, the concrete yard calculator converts a finished volume into a clean ready-mix order quantity.

Worked Examples and How Much to Over-Order

Example 1: Patio Slab

12 ft × 16 ft × 4 in thick: depth = 4 ÷ 12 = 0.333 ft. Volume = 12 × 16 × 0.333 = 63.9 ft³ ÷ 27 = 2.37 cubic yards.

Example 2: Round Column

12-inch (1 ft) diameter sonotube, 4 ft deep: radius = 0.5 ft. Volume = π × 0.5² × 4 = 3.14 ft³ ÷ 27 = 0.116 cubic yards.

Adding a Waste Factor

Add 10% on top of the calculated volume for typical slabs and footings, 15% for footings poured against rough hand-dug earth, and as little as 5% for large flatwork on a screeded base. A small surplus is cheap insurance; running short mid-pour forces a cold joint, which is a permanent weak plane. For anything over 1 cubic yard, ready-mix delivered by truck is cheaper and more consistent than mixing bags.

Sources & References

ACI 318-19: Building Code Requirements for Structural Concrete — American Concrete Institute
ASTM C94/C94M: Standard Specification for Ready-Mixed Concrete — ASTM International
PCA: Design and Control of Concrete Mixtures (16th Edition) — Portland Cement Association