How this instrument works
Premixed bagged concrete (like Quikrete or Sakrete) is labeled with a "yield" — the volume of finished, compacted concrete one bag produces once mixed with the correct amount of water. To estimate bags needed for a project, you first calculate the total volume of concrete required from the pour's dimensions, then divide by the bag's yield and round up, since you can't buy a fraction of a bag.
Bag yield depends on bag weight: an 80 lb bag is commonly labeled to yield about 0.60 cubic feet, a 60 lb bag about 0.45 cubic feet, and a 40 lb bag about 0.30 cubic feet — the standard chart used across major premixed-concrete brands. Always check your specific product's actual printed yield rather than assuming these figures apply universally, since formulations and yields can vary by brand and product line.
This calculator converts your slab or footing's length, width, and thickness (entered in feet and inches) into cubic feet of concrete needed, then divides by whatever bag yield you enter and rounds up to the next whole bag.
- Enter the pour area's length and width in feet.
- Enter the concrete thickness in inches.
- Enter your bag's printed yield in cubic feet — the default assumes a standard 80 lb bag at 0.60 cu ft; adjust it to match your actual product.
- Read the total concrete volume needed and the number of bags to buy.
A 10 x 10 ft slab, 4 inches thick, using 80 lb bags
A homeowner is pouring a 10 ft by 10 ft slab at 4 in thick, using standard 80 lb premixed concrete bags (0.60 cu ft yield each). Volume needed: 10 x 10 x (4/12) = 33.333 cu ft. Bags needed: ceil(33.333 / 0.60) = ceil(55.556) = 56 bags — rounding up since a partial bag isn't usable on its own.
The same 4 in thickness on a smaller 8 x 6 ft pad, using 60 lb bags (0.45 cu ft yield) instead, shows how bag size changes the count even for a smaller pour: volume = 8 x 6 x (4/12) = 16 cu ft, and bags = ceil(16/0.45) = ceil(35.556) = 36 bags — proportionally more bags per cubic foot than the 80 lb example, since each smaller bag contributes less volume.
Questions
Where do I find my bag's actual yield if it's not 0.60 cu ft?
Check the bag's label or the manufacturer's technical data sheet — most premixed concrete products print their yield directly on the packaging. Common standard yields are 0.60 cu ft for an 80 lb bag, 0.45 cu ft for a 60 lb bag, and 0.30 cu ft for a 40 lb bag, but always confirm against your specific product since formulations vary.
Should I buy extra bags beyond the calculated number?
Many contractors and DIYers add a small buffer — often a bag or two extra — to cover minor spillage, uneven subgrade, or measurement variance, especially on larger pours where running short mid-pour is a real problem. This calculator gives the theoretical minimum; how much buffer to add depends on your comfort margin and the project's size.
Is bagged premixed concrete the same as ready-mix delivered by truck?
They're both concrete, but bagged premix is meant for smaller DIY-scale pours you mix yourself with a wheelbarrow or mixer, while ready-mix trucks deliver already-mixed concrete for larger pours where hand-mixing dozens of bags would be impractical. Once a pour gets much larger than a small slab or footing, ready-mix delivery is usually more cost-effective.
Does thickness really matter that much for bag count?
Yes — volume scales directly with thickness, so doubling your slab thickness doubles the concrete volume and roughly doubles the bag count for the same footprint. Double-check your project's required thickness (often specified by a structural plan or local code) before ordering, since undershooting it wastes a trip back to the store and overshooting it wastes money.