Concrete yardage calculator
Cubic yards for a slab or footing, with waste, and the bag count if you are mixing it yourself.
Order short and the pour stops with a cold joint you will be explaining for the life of the slab. Order long and you have paid for material sitting in a truck. Neither gives you time to think once the drum is turning.
Enter the dimensions and a waste allowance. Thickness is in inches because that is how slabs are specified, and the conversion to yards is where the arithmetic usually goes wrong.
4 in is standard for a residential walkway or patio. Driveways want more.
5-10% on prepared subgrade. More on uneven ground or footings in soft soil.
What to order
| Bag size | Yield each | Bags needed |
|---|---|---|
| 50 lb | 0.375 cu ft | 587 |
| 60 lb | 0.45 cu ft | 489 |
| 80 lb | 0.6 cu ft | 367 |
A cubic yard is 27 cubic feet, not 9. That one conversion accounts for most bad concrete orders. Check your supplier's short-load minimum before deciding 8.15 yards is cheaper to order than the next whole truck.
A cubic yard is 27 cubic feet, not 9. That single conversion accounts for most bad concrete orders.
Five to ten percent waste suits a flat slab on well-prepared subgrade. Go higher on uneven ground, where low spots swallow concrete invisibly, and higher again on footings dug in soft or crumbly soil where overdig is real.
Bag counts are for small pours and repairs. Check your supplier's short-load fee before deciding that 6.2 yards is cheaper to order than 7.
The reasoning behind these numbers is in How to estimate a concrete job.