Concrete Bag Calculator
One volume in, four answers out: how many 40, 50, 60, and 80 lb bags of pre-blended concrete mix the job takes, computed from manufacturer yield data with a waste allowance and an optional per-bag cost.
Volume to fill
Example: 10 cu ft with 10% waste needs 19 × 80 lb bags.
Bag counts are purchasing estimates only; whether the mix or thickness suits the job structurally is a question for a licensed professional.
How a volume becomes a bag count
For each size, bags = ceil(volume × (1 + waste%) ÷ yield per bag). The worked 10 cu ft project grows to 11 cu ft with waste, and the engine-computed counts
are:
- 40 lb bags (0.3 cu ft each): 37 bags, 0.1 cu ft spare
- 50 lb bags (0.38 cu ft each): 30 bags, 0.25 cu ft spare
- 60 lb bags (0.45 cu ft each): 25 bags, 0.25 cu ft spare
- 80 lb bags (0.6 cu ft each): 19 bags, 0.4 cu ft spare
Waste is applied to the volume before the round-up to whole bags. Doing it the other way — padding the finished bag count — double-charges the margin on small jobs.
Yields, per the data sheet
Every size of Quikrete Concrete Mix places 0.0075 cu ft per pound: 40 lb → 0.3 cu ft, 50 lb → 0.38 cu ft, 60 lb → 0.45 cu ft, 80 lb → 0.6 cu ft. That regularity is why doubling the bag weight exactly halves the count before rounding.
Frequently asked questions
Where do the yield figures per bag come from?
From the manufacturer: the Quikrete Concrete Mix (No. 1101) data sheet lists 0.30, 0.375, 0.45, and 0.60 cu ft of placed concrete for the 40, 50, 60, and 80 lb bags. Other brands are close but not identical — check your bag if you are using a different mix.
Why do all four sizes show at once?
Because the right size is a trade-off: heavier bags mean fewer to carry and mix but each lift is harder. Seeing 40 through 80 lb side by side lets you weigh bag count against back strain and per-bag price at your store.
I only know my project in cubic yards — do I convert?
No, just switch the unit selector to cubic yards; the tool multiplies by 27 internally. If you have slab dimensions instead of a volume, run the concrete slab calculator first and bring its cubic-feet figure here.
Does yield change with how much water I add?
The manufacturer states yields as approximate for a properly mixed bag. Overwatering weakens concrete more than it stretches it — mix to the bag instructions and let the waste allowance absorb the variation.
Everything computes locally in your browser; no volume you enter is stored or sent. Sources for the yield constants are cited on the methodology page and in the engine itself.