Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
80lb bags needed
10
Total cubic feet
5.33
Total bag weight
800
lbs
Exact bags before rounding
9.78
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How to use this
- 1Enter length (ft).
- 2Enter width (ft).
- 3Enter thickness (in).
- 4Enter waste factor (%).
- 5Read your 80lb bags needed on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
An 80lb bag of ready-mix concrete yields about 0.6 cubic feet once mixed, which is the standard coverage figure printed on Quikrete and Sakrete bags alike. For small jobs like fence post footings, a mailbox base, or a short walkway patch, bagged concrete is far more practical than ordering a ready-mix truck with a load minimum. This calculator takes your pour's length, width, and thickness, computes total cubic feet, divides by 0.6 to get a raw bag count, then rounds up and adds a waste allowance since spilled powder, over-mixed batches, and slightly-thicker-than-planned pours are the norm on hand-mixed jobs. Buying bagged concrete by the pallet (usually 42 or 56 bags) often comes with a per-bag discount, so the calculator also flags how close you are to a pallet quantity. Always round up to a whole bag; there is no such thing as ordering 11.4 bags, and running one bag short mid-pour on a footing that needs to cure monolithically is a bigger problem than having one extra bag left over.
Worked example
Using the values the calculator loads with:
Inputs
- Length: 4 ft
- Width: 4 ft
- Thickness: 4 in
- Waste factor: 10 %
Results
- 80lb bags needed: 10
- Total cubic feet: 5.33
- Total bag weight: 800
- Exact bags before rounding: 9.78
What each field means
Inputs
- Length (ft)
- The length used in the calculation, measured in ft. Starts at 4 ft so you have a working example on load.
- Width (ft)
- The width used in the calculation, measured in ft. Starts at 4 ft so you have a working example on load.
- Thickness (in)
- The thickness used in the calculation, measured in in. Starts at 4 in so you have a working example on load. Accepted range: 1–24 in.
- Waste factor (%)
- The waste factor used in the calculation, measured in %. Starts at 10 % so you have a working example on load. Accepted range: 0–30 %.
Results
- 80lb bags needed
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total cubic feet
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total bag weight
- lbs
- Exact bags before rounding
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Why 0.6 cubic feet per bag?
That's the manufacturer-stated mixed yield for a standard 80lb bag of concrete mix — the bag itself weighs 80lb of dry powder and aggregate, but once water is added and it's fully mixed, it occupies about 0.6 cubic feet.
How does this compare to 60lb or 50lb bags?
60lb bags yield about 0.45 cubic feet and 50lb bags about 0.375 cubic feet — proportionally less than the 80lb bag's 0.6 cubic feet, so you need more bags but each is lighter to carry, which matters for one-person jobs.
Should I round up or down on the bag count?
Always round up. A partial bag can't be bought, and running short mid-pour on a footing or post hole means either an unplanned trip to the store or a cold joint that weakens the cure.
Is bagged concrete as strong as ready-mix delivered concrete?
Yes, general-purpose bagged mixes typically cure to 4,000 PSI, comparable to a standard ready-mix truck load, as long as you follow the water ratio on the bag and don't over-water the mix.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
60lb Concrete Bags Calculator
Bag count for jobs sized around the lighter, easier-to-carry 60lb mix.
Concrete Cubic Yards Calculator
Convert a slab, footing, or pad's dimensions straight into cubic yards of ready-mix.
Concrete for Fence Posts Calculator
Bag count for setting a whole run of fence posts in concrete footings.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). 80lb Concrete Bags Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/concrete-bags-80lb-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/concrete-bags-80lb-calculator" target="_blank" rel="noopener">80lb Concrete Bags Calculator — RevenueLab</a> (2026).</p>
Source: [80lb Concrete Bags Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/concrete-bags-80lb-calculator) (2026).