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Concrete Calculator

Concrete Calculator

Estimate concrete for a slab, footing, or round column in cubic yards, cubic meters, and 60 lb or 80 lb bags.

ft
ft
in

Number of identical slabs, footings, or columns.

%

Many contractors add 5 to 10% for spillage and uneven ground.

Results appear as you type.

How to use

  1. Pick the shape you are pouring and choose US or metric units.
  2. Enter the dimensions. Slab thickness is in inches (or centimeters).
  3. Add a quantity if you have several identical pours, and an extra percentage for waste.
  4. Order by the cubic yard for large pours, or use the bag count for small jobs.

Formula

slab or footing: volume = length × width × thickness
column: volume = π × (diameter / 2)² × height
cubic yards = cubic feet / 27
80 lb bags = cubic feet / 0.60 (rounded up)
60 lb bags = cubic feet / 0.45 (rounded up)

Worked examples

10 × 10 ft patio slab, 4 in thick

33.33 cu ft, which is 1.23 cubic yards. That is 56 bags of 80 lb mix or 75 bags of 60 lb mix.

Wall footing

20 ft long, 12 in wide, 8 in deep, plus 10% waste, is 14.67 cu ft (0.54 cu yd), or 25 bags of 80 lb mix.

Four post holes

Four round holes 12 in across and 4 ft deep hold 12.57 cu ft, or 21 bags of 80 lb mix.

Assumptions

  • Bag yields are 0.60 cu ft for an 80 lb bag and 0.45 cu ft for a 60 lb bag, the figures printed on common pre-mixed concrete bags. Check your bag.
  • The calculator does not subtract rebar, pipes, or gravel base.
  • This is a material estimate only. Structural footings and slabs should follow local code and a qualified professional.

FAQ

How many 80 lb bags of concrete are in a cubic yard?

A cubic yard is 27 cubic feet. At 0.60 cu ft per bag that is 45 bags of 80 lb mix.

How many 60 lb bags make a cubic yard?

At 0.45 cu ft per bag, one cubic yard takes 60 bags of 60 lb mix.

How thick should a concrete slab be?

Patios and walkways are often 4 inches thick. Driveways and slabs that carry vehicles are often thicker. Follow local code or your contractor for your project.

Should I order extra concrete?

Running short mid-pour is a bigger problem than a little leftover, so many people add 5 to 10% for waste.

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