Concrete footings and slabs
Enter the footings or the slab. This works out the cubic yards and the bags that pour it.
Advanced settings80 lb bags
Buy
8bags, 80 lb
Cubic feet
4.71
Cubic yards
0.175
By bag size
- 40 lb bags0.30 ft³ per bag
- 16
- 60 lb bags0.45 ft³ per bag
- 11
- 80 lb bags0.60 ft³ per bag
- 8
Where to buy this
- 8 × 80 lb bagsHome DepotLowe's
Buy one more bag than the table says — concrete you did not need is cheaper than a second trip mid-pour.
Plain search links, nothing sponsored. Prices and stock are the shop's, and a local lumberyard will usually beat both on solid stock.
For anything past a couple of yards, ready-mix delivered by truck is usually both cheaper and far less labour than mixing that many bags by hand.
Worked example: three post holes
Three holes 12" across and 24" deep hold 4.71 cubic feet of concrete, or 0.175 cubic yards: 8 bags of 80 lb premix.
The slab tab opens on 10 × 10 ft at 4" thick, which is 1.23 cubic yards, or 56 bags of 80 lb premix.
- 80 lb bags, the holes
- 8
- 80 lb bags, the slab
- 56
- 60 lb bags, the holes
- 11
- 60 lb bags, the slab
- 75
- 40 lb bags, the holes
- 16
- 40 lb bags, the slab
- 112
These are the figures the calculator above opens on. Change any field and it works the same problem for your numbers.
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About mixing concrete
- How many bags make a cubic yard?
- 45 bags of 80 lb, 60 bags of 60 lb, or 90 bags of 40 lb — these are the yields Quikrete and Sakrete print on the bag itself, not an estimate, which is why they come out to round numbers. Smaller bags cost more per cubic foot, so the tradeoff is money against how much you want to lift.
- Why is a footing's volume based on its diameter, not its width?
- Because a post footing is normally dug or formed round, with a post-hole digger or a cardboard tube form, so the volume is a cylinder — π times the radius squared times the depth — rather than the length-times-width-times-height of a slab.
- Should I round up?
- Yes, by at least one extra bag per footing and a few percent on a slab. Bags settle air out unevenly, a form is rarely perfectly straight-sided, and running short partway through a pour with the mix already wet is a much worse afternoon than one leftover bag.
- When should I order ready-mix instead of mixing bags?
- Past about a cubic yard, most people are better off with a delivered truck or a trailer-mounted mixer. A yard of concrete is 45 bags of 80 lb — over 3,600 lb to move, mix and place by hand — and ready-mix cures more consistently because the whole pour goes in at once rather than bag by bag.
You might also need
- Concrete screw lengthLength and embedment for a concrete screw, the bit that goes with it, and how deep to drill.
- Deck and fence takeoffBoards, joists, posts, pickets, screws and bags of concrete, with the gaps between boards properly counted.
- Fence calculator: post spacingPost count and the actual on-centre spacing for any run and maximum span.
- Concrete block and brickBlocks or bricks for a wall with waste, the bags of mortar at your bag's own yield, and vertical rebar at your spacing.
- Gravel and mulchCubic yards, tons and bags of gravel, crushed stone, sand, topsoil or mulch for a rectangle, circle or triangle at a depth.
- Paver patioPavers to buy with waste for the pattern, tons of base gravel, bedding sand and feet of edge restraint for a patio.