Calculate concrete volume for slabs, columns, tubes, curbs, and stairs in cubic yards and cubic feet. Estimate package count from the yield you enter and dry-mix weight from that count and the bag weight you enter.
Inputs and method
Choose a shape and enter its dimensions, quantity, waste allowance, yield per bag, and bag weight. Shape volume is calculated in cubic feet, waste is applied once, and bags are rounded up only after division by the entered yield. Estimated dry-mix weight is the exact rounded bag count multiplied by the entered bag weight.
Calculations retain full floating-point precision until the labeled display step. Counts and packages use an explicit upward ceiling only where a whole purchase unit is required.
Interpreting the estimate
Use the result as a planning value and keep input precision consistent with the measurements or source data you have. Small displayed differences can come from final-place rounding; intermediate values are not rounded.
Assumptions and limits
This is a geometric material estimate. The 0.6 cu ft yield and 80 lb weight shown initially are separate, editable planning assumptions. For metric cubic-meter quantities, use the concrete volume calculator; for masonry walls on top of the slab, see the brick calculator; and for concrete stair geometry, use the stair calculator. An 80 lb package does not have a universal yield: use the yield and weight printed for the product you plan to buy. The weight result is package count times entered package weight, not a concrete-density calculation. Product yield, subgrade, forms, spillage, reinforcement, placement, and structural requirements are separate.
Rejecting empty, invalid numeric, prohibited negative, zero-denominator, impossible, or unsupported inputs prevents the page from presenting a misleading numeric result.
Break a mixed project into measured shapes
Run each slab, column, or other distinct shape using its own measured dimensions, then keep a subtotal list before combining the required volume. Compare waste allowance separately from geometry. For bags, use the product’s stated yield as your entered assumption; changing bag weight alone is not a substitute for confirming its yield.
Turn a mixed job into volume subtotals
Use a short takeoff sheet before combining a project:
| Piece | Record for that piece | Keep separate afterward |
|---|---|---|
| Rectangular slab or footing | Its own length, width, height, units, and quantity | Its calculated volume |
| Column or ring | The selected shape and its active diameters/height | Its calculated volume |
| Stair or curb section | The fields specific to that selected shape | Its calculated volume |
Add compatible volume subtotals only after each piece is measured. Retain waste allowance and product yield outside the geometry record so you can see whether a changed purchase quantity comes from dimensions or an ordering assumption.
Sources
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31pr — Industry guidance to order roughly 4-10% more than the calculated quantity, supporting the page’s one-time waste allowance.
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Farm Construction — Slab volume formula (cubic yards = length x width x thickness / 324, with 27 cu ft per cubic yard).
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Concrete — Manufacturer-published per-bag yields (e.g., 80 lb mix yields about 0.60 cu ft), supporting the editable yield and weight assumptions and product-specific bag counts.