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Concrete Calculator

Estimate concrete for rectangular slabs or round columns, with an allowance and bag equivalents.

Your project measurements

ft
ft
in
%
$

Results update as you type. U.S. units. Defaults are editable planning examples. Use product labels and supplier specifications.

Your material plan

Enter your measurements to see your plan.

A quantity estimate, not a supplier quote. Confirm order increments, delivery and project specifications.

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How this calculation works

Enter measurements above to see the worked calculation.

Rectangular slabs and round columns

For a slab, enter length and width in feet and thickness in inches. For a round column, length becomes diameter in feet and thickness becomes height in inches; width is unused. The count repeats identical sections only. For different shapes, calculate each section separately and sum the net volumes.

Volume, allowance and an order are different

Net volume is the space to fill. The allowance adds extra material for variation in excavation, forms and handling. A supplier may then round the order to its available increments. Our decimal result does not apply that final supplier rounding. For multiple sections, calculate each section and add the unrounded volumes before ordering.

Bag equivalents are alternatives

The displayed 60-lb and 80-lb equivalents use illustrative yields of 0.45 and 0.60 cubic feet. They are alternatives to a ready-mix delivery, not additional materials. A bag’s weight alone does not determine its yield. Check the product you will actually buy.

Product reference: QUIKRETE concrete mix technical data. Confirm the current label for your chosen product.

Choose how to buy your concrete

Compare bagged concrete with a ready-mix delivery, including handling and fees. If buying bags, see our QUIKRETE vs. Sakrete product comparison for published yields and a project-cost example.

Make the estimate your own

Measure the actual area, choose your product and update the allowance. Costs use the price you enter. Delivery, tax, labor and preparation are excluded unless this tool has a separate field for them. The result rounds whole packages up; displayed decimal quantities are not supplier order increments.

Before you order

  • Check dimensions and units, including depth and openings.
  • Confirm the selected product’s coverage, yield or density.
  • Ask your supplier about package sizes, minimum orders and delivery access.
  • Keep a copy of your measurements with your material plan.

Method v1.0 · Updated October 23, 2026. Read our methodology.