Common jobs
| Job | Size | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|---|
| Patio slab | 10' × 10' × 4" | 1.36 | 62 | 82 |
| Shed pad | 8' × 12' × 4" | 1.30 | 59 | 79 |
| Garage floor | 24' × 24' × 6" | 11.73 | 528 | 704 |
| AC pad | 3' × 4' × 4" | 0.16 | 8 | 10 |
| Wall footing | 20' long, 16" wide, 8" deep | 0.72 | 33 | 44 |
| Deck piers | 6 piers, 10" across, 3' deep | 0.40 | 18 | 24 |
| Fence post holes | 10 holes, 8" across, 2' deep | 0.28 | 13 | 18 |
| Mailbox post | 1 hole, 10" across, 2' deep | 0.04 | 2 | 3 |
How much concrete is in a bag
An 80 lb bag of concrete mix makes about 0.60 cubic feet once it's mixed. A 60 lb bag makes about 0.45 cubic feet. A cubic yard is 27 cubic feet, so it takes 45 of the 80 lb bags, or 60 of the 60 lb bags.
The calculator rounds bags up. You can't buy part of a bag, and running out halfway through a pour is worse than one bag left over.
How this is worked out
For a slab, pad or footing, length times width times thickness gives the volume. For a round pier, it's pi times the radius squared times the depth, times the number of piers. Every length is rounded to the nearest sixteenth of an inch first, and pi is 355/113, the same value Handyman Calc uses.
Then the waste is added: 10% unless you change it. That covers spills, an uneven base and forms that bow. The math is done in exact fractions, so a job that comes to a whole number of bags isn't pushed up one by a rounding error.
Want it already worked out? There's a concrete bags chart for slabs from 4 × 4 to 12 × 16 ft, with a PDF to print.
On your phone, on the job site
This is the concrete screen from Handyman Calc, our free construction calculator. The app also prices the job from your bag or yard price, adds fourteen more calculators, and works with no signal.
▶ Try it in your browser ▶ Get it on Google Play
Charts worked out with the same math:
- how many bags of concrete a slab takes
- how many sheets of drywall a room takes
- a fraction to decimal chart for inches
- how much paint a room takes
- how much mulch a bed takes
- a roof pitch chart
- how many steps a rise takes
- the diagonal that squares a frame
- board feet for common lumber
More calculators: