Rectangular projects
Slabs and footings
Volume = length × width × depth
Use consistent units. When working in feet, divide thickness in inches by 12 before multiplying.
Concrete Calculator
Estimate ready-mix volume, full bags, waste, and optional cost for slabs, footings, or round post holes.
Choose a project shape and enter measurements below. Results update as you type.
01 — Project setup
What are you pouring?
02 — Measurements
Enter project dimensions
ft
ft
in
Length and width use feet; slab or footing thickness uses inches.
03 — Site allowance
Waste allowance
Covers spills, uneven subgrade, and ordering margin.
Add optional local prices +
$ / yd³
$ / m³
$ / bag
Your results update as dimensions change.
Round projects
Post holes and columns
Volume = π × radius² × depth × holes
Radius is half the diameter. This estimate uses the complete cylindrical hole volume before waste.
Published concrete guides
GuideConcrete Slab Cost: Volume, Bags, Ready-Mix, and Site ScopeCalculate slab volume for common sizes, then separate concrete material from site prep, reinforcement, finishing, delivery, and labor assumptions.Read guide →GuideHow Much Concrete Do I Need per Fence Post?Estimate concrete for fence-post holes with a cylinder formula, bag-yield checks, and links to the fence and concrete calculators.Read guide →
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Concrete questions
Before you order
01How do I calculate concrete for a slab?+
Multiply slab length by width by thickness, using consistent units. For imperial measurements, convert thickness from inches to feet before multiplying. The calculator handles this conversion and adds your selected waste allowance.
02How many bags of concrete do I need?+
Divide the total required cubic feet by the approximate yield of one bag, then round up. Typical yields are about 0.30 ft³ for 40 lb, 0.45 ft³ for 60 lb, and 0.60 ft³ for 80 lb bags. Always confirm the package yield.
03How do I convert cubic feet to cubic yards?+
Divide cubic feet by 27 because one cubic yard contains 27 cubic feet. For example, 54 cubic feet equals 2 cubic yards.
04How much waste should I add for concrete?+
Ten percent is a practical planning allowance for many small pours. A well-formed, level project may need less, while uneven excavation, spillage, or uncertain dimensions may justify 15 percent.
05How thick should a concrete slab be?+
Thickness depends on loading, reinforcement, base preparation, soil, and local code. Four inches is common for many residential walkways and patios, but vehicle slabs or structural work may require a different engineered specification.
06Can I calculate concrete for post holes?+
Yes. Choose Post hole, enter the round hole diameter, depth, and number of holes. The calculator applies the cylinder formula to the complete set.
07What units does this concrete calculator support?+
Use feet with inches for imperial projects or meters with centimeters for metric projects. Results are shown together in cubic feet, cubic yards, and cubic meters.