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Concrete Calculator

This concrete calculator converts slab or column dimensions into cubic yards, cubic feet, and 60- or 80-pound bag counts.

Shape

Enter every dimension in the same unit.

Default 10%. Use 0% for a raw volume with no extra.

A 4-inch slab is 0.333 ft (4 ÷ 12). Switch units to inches to enter 4.

Concrete estimate

Cubic feet (with waste)
36.667
Cubic yards (with waste)
1.358
60-lb bags (≈ 0.45 cu ft)
82
80-lb bags (≈ 0.60 cu ft)
62

Volume before waste: 33.333 cu ft (1.235 cu yd).

Materials estimate only—not a contractor bid. Bag counts are rounded up. Rebar, forms, labor, and delivery are not included.

How to use

  1. Choose a rectangular slab or a round column.
  2. Enter length, width, and depth (or diameter and height) in feet or inches.
  3. Set a waste percent. The default is 10%. Use 0% for raw volume.
  4. Read cubic yards and how many bags to buy. Rebar, forms, and labor are not included.

Formula

Slab volume in cubic feet is length × width × depth after converting inches to feet. A round column is π × radius² × height. Cubic yards = cubic feet ÷ 27, then multiply by (1 + waste / 100). An 80-lb bag is 0.60 cubic feet and a 60-lb bag is 0.45.

Example. A 10 ft by 10 ft slab at 4 inches is 10 × 10 × (4 ÷ 12) = 33.33 cubic feet, or about 1.23 cubic yards before waste.

Frequently asked questions

How do I calculate how much concrete I need?

Multiply length × width × depth in feet, then divide by 27 to get cubic yards. Add 5–10% waste for over-excavation and spillage.

How many 80 lb bags are in a cubic yard?

An 80-lb bag is about 0.60 cubic feet. One cubic yard (27 cu ft) is roughly 45 bags of 80-lb mix.

What thickness should a slab be?

Walkways are often 4 inches; driveways 4–6 inches. Confirm with your local code or a contractor.

Does this include rebar or forms?

No. It estimates concrete volume and bag count only.

Can I mix units?

Enter all dimensions in the same unit (feet or inches). The tool converts to yards and bags.

Should I add a waste factor?

Yes. 5–10% is common for slabs to cover over-excavation, uneven subgrade, and spillage. This calculator defaults to 10%; set it to 0% for a raw volume.

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