Concrete Cubic Yard Calculator
Estimate concrete volume in cubic yards and cubic feet from length, width, and thickness. Add a waste factor and an optional bag count for small placements.
Enter your values, then press Calculate.
How to calculate
Enter the length and width of the placement and the thickness of the slab, footing, or wall. Thickness is usually measured in inches in the field. Choose a waste factor for over-excavation, over-pour, and pump residue. The calculator converts everything to feet, multiplies for cubic feet, then divides by 27 for cubic yards.
Formula
Volume (ft³) = length (ft) × width (ft) × thickness (ft). Cubic yards = ft³ ÷ 27. Waste multiplies the neat volume. Bag counts use typical yields of 0.30 ft³ (40 lb), 0.45 ft³ (60 lb), and 0.60 ft³ (80 lb).
Common use cases
- Residential and commercial slab pours
- Footings, sidewalks, and pads
- Quick field checks before calling the ready-mix plant
- Bagged concrete estimates for small patches
Assumptions
- The placement is a rectangular prism: length × width × thickness, all converted to feet before dividing by 27.
- Thickness is the pour depth you intend to fill, not the subgrade cut and not a thickened edge.
- Bag yields are typical published values (0.30 / 0.45 / 0.60 ft³ for 40 / 60 / 80 lb bags), not a brand mix design.
- Waste multiplies neat volume for over-pour, pump leftover, and irregular subgrade. It is not a strength factor.
Limitations
- Does not subtract blockouts, pipes, or void formers.
- Does not add thickened edges, turndowns, or stem walls — run those as a second placement.
- Does not convert volume to asphalt or aggregate tons. Those materials need density, not 27 ft³ per yard of concrete.
- Does not recommend a mix, slump, or bag brand.
Worked examples
10x10 slab at 4 inches with 10% waste
A 10 ft × 10 ft × 4 in slab is a common patio check. Thickness 4 in = 0.333 ft. Neat volume 33.33 ft³ = 1.235 yd³. Ten percent waste brings the order to 1.358 yd³, which is why plants usually will not quote the neat 1.23 without a waste line.
1. Convert thickness to feet
4 in ÷ 12 = 0.3333 ft
2. Neat volume in cubic feet
10 ft × 10 ft × 0.3333 ft = 33.3333 ft³
3. Convert to cubic yards
33.3333 ft³ ÷ 27 = 1.2346 yd³
4. Apply waste factor
1.2346 × (1 + 10%) = 1.358 yd³
5. Bag count from typical yield
ceil(36.6667 ft³ ÷ 0.6 ft³/80 lb bag) = 62 bags
Decimal feet dimensions
1. Convert thickness to feet
6 in ÷ 12 = 0.5 ft
2. Neat volume in cubic feet
12.5 ft × 8.25 ft × 0.5 ft = 51.5625 ft³
3. Convert to cubic yards
51.5625 ft³ ÷ 27 = 1.9097 yd³
4. Apply waste factor
1.9097 × (1 + 0%) = 1.9097 yd³
5. Bag count from typical yield
ceil(51.5625 ft³ ÷ 0.45 ft³/60 lb bag) = 115 bags
Cubic yards from a rectangular placement
Volume (yd³) = length × width × thickness (all in feet) ÷ 27. A 10 ft × 10 ft × 4 in slab is 10 × 10 × (4/12) ÷ 27 = 1.235 yd³ before waste. Ready-mix in the U.S. is ordered in cubic yards. This is a rectangular prism; it does not subtract blockouts, add thickened edges, or apply a mix design. Bag counts use typical published yields and are not a brand guarantee.
Waste and thickness units
Enter thickness in inches or feet; the calculator converts to feet before dividing by 27. 5–10% waste is common for slabs on grade; use more for irregular subgrade, thickened footings, or pumped placements. Confirm with the supplier. This page does not convert to asphalt or base-rock tons — those materials use density, not 27 ft³ per yard of concrete.
When a second takeoff is required
A driveway with a 4 in slab and a 12 in thickened edge is two prisms, not one average thickness. Calculate the slab rectangle, then the edge as its own length × width × thickness, and add the yards. Curved walks and circular pads are also outside this rectangle; split them into rectangles you can measure, or use a plan takeoff for the area and enter that area as length × 1 ft width only if you have already converted area to an equivalent rectangle.
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FAQ
How many cubic yards of concrete do I need?
Multiply length × width × thickness in feet, then divide by 27. A 10 ft × 10 ft × 4 in slab is 1.235 cubic yards before waste.
Why divide by 27?
One cubic yard is 27 cubic feet (3 ft × 3 ft × 3 ft). Ready-mix is ordered in cubic yards in the U.S.
How much waste should I add?
5–10% is common for slabs on grade. Use more for irregular subgrade, thick footings, or pumped placements. Confirm with the supplier.
Are bag counts exact?
No. Bag yields vary by brand and mix. The values here are typical published yields for estimating only.
Can I use this for a circular pad?
Not directly. This tool is a rectangle. For a round pad, compute area as πr², treat that area as square feet, and convert thickness to feet so volume ft³ = area × thickness, then divide by 27. The live form does not accept a radius.
Disclaimer
These calculators are estimating tools for planning and field checks. They are not a substitute for approved plans, specifications, licensed professional engineering, or governing standards. Confirm densities, waste factors, and yields with your supplier and project documents.