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Concrete Calculator

Estimate cubic yards, common bag sizes, and cost for slabs, footings, walls, and round columns.

Calculated and reviewed by HomeTaskKit Editorial Team ·
Quick answer

Concrete volume is length × width × depth for rectangular work, with the result converted to cubic yards. Add a project-appropriate allowance, then compare ready-mix volume with full-bag quantities.

Your planning estimate1.36 yd³ / 62 × 80-lb bags

33.33 cu ft including 10% allowance.

Measured need1.23 yd³ geometric volumeBuy / plan1.36 yd³ / 62 full bags
Formula: length × width × depth × quantity ÷ 27 × allowance
Shopping list
  • Concrete mix62 80-lb bags

Large pours may be more practical as ready-mix. Confirm minimum loads, short-load fees, reinforcement, subbase, and mix specification.

Use it well

Step by step

  1. 1

    Choose the project shape and enter finished dimensions, including the actual slab or footing depth.

  2. 2

    Add separate sections when thickness or shape changes instead of averaging unlike areas.

  3. 3

    Apply a small allowance for grade variation and spills, then round bags up or confirm the ready-mix supplier’s minimum order.

Worked example

Check the estimate before you buy

Estimate concrete volume for slabs, footings, walls, and round columns, then compare cubic yards with common bag sizes.

Example

A 10 × 10 ft slab at 4 in thick is 33.33 cubic feet, or 1.23 cubic yards before waste. A 10% allowance raises the planning order to about 1.36 cubic yards.

How the calculation works

Rectangular pours use length × width × thickness. Round columns use π × radius² × height. The result converts cubic feet to cubic yards and applies the selected allowance before bag yields are used.

Planning checklist

Before you place the order

  • Use the finished, compacted dimensions—not the excavation guess.
  • Price bagged mix and ready-mix separately; delivery minimums and short-load fees matter.
  • Confirm mix specification, reinforcement, base preparation, and local requirements before the pour.
Common questions

Concrete Calculator FAQ

Should I buy exactly the calculated amount of concrete?

Usually no. Cuts, spillage, breakage, uneven surfaces, batch matching, and package rounding can increase the order. Use the editable allowance and confirm the product label.

Why does the result round up?

Stores sell full bags, boxes, cans, rolls, panels, or pieces. The tool keeps the mathematical amount visible, then rounds the purchasing quantity up separately.

How many 80 lb bags make one cubic yard?

Using a typical 0.60 cubic-foot yield, one cubic yard requires about 45 bags before waste. Always use the yield printed on the selected product.

When should I order ready-mix?

Ready-mix is often more practical when the bag count, mixing time, consistency, or continuous-pour requirement becomes difficult. Ask suppliers about minimums and unloading time.

Source & method

Reference: HomeTaskKit material-estimating method. Results are practical estimates; complete labels, package directions, product specifications, and qualified professional advice take priority.