Concrete Bag Calculator
Bags of concrete mix are the practical way to buy small volumes: footing pads, post holes, stepping stones, a patch or two. Tell this calculator the area and depth, or a volume straight from another estimate, and it counts the bags — rounded up, because nobody pours half a bag. Yields come prefilled with typical values, and you can edit them after checking the bag you actually plan to buy. As always, the result is an estimate for planning, not a purchase order.
Step by step
How to use this calculator
- Choose your input. "Area and depth" fits pads and slabs you have measured; "Direct volume" takes a volume in cubic yards if you already have one.
- Enter the numbers. For area and depth, measure the surface and the thickness you want. For direct volume, paste the cubic yards from any other estimate.
- Pick a bag size. The 40, 50, 60 and 80 lb options come with typical yields already filled in — check the bag and adjust if yours differs, or choose the custom option and enter your own.
- Set an allowance and read the count. Extra bags for spillage and uneven ground are common; 10% is a frequent example. The result rounds up to whole bags and shows the total weight, which matters more than you think at 60 bags.
Formulas
- Volume: area (ft²) × depth (in) ÷ 12 = ft³; cubic yards = ft³ ÷ 27.
- Bags: total = volume with allowance ÷ yield per bag, always rounded up to the next whole bag.
- Weight: total weight = bag count × bag weight.
- Typical yields (examples, check the bag): 40 lb ≈ 0.30 ft³, 50 lb ≈ 0.375 ft³, 60 lb ≈ 0.45 ft³, 80 lb ≈ 0.6 ft³.
- Metric: enter area in m² and depth in cm, or a volume in m³; 1 m³ ≈ 35.3 ft³ of volume needs just as many bags, whichever unit you quote it in.
Worked example
Worked Example
A 10 × 10 ft pad, 4 inches thick, 80 lb bags
10 × 10 × 4 ÷ 12 = 33.3 ft³. With a 10% allowance that is 36.7 ft³, and 36.7 ÷ 0.6 comes to 61.1 — so 62 bags, just over half a cubic pallet's worth. Your delivery person will appreciate knowing that number in advance.
A strip footing worth 0.66 yd³, 60 lb bags
0.66 yd³ is 17.8 ft³; with 10% extra it is 19.6 ft³. At a typical 0.45 ft³ per 60 lb bag, that is 43.5 — round up to 44 bags.
Metric volume, 0.9 m³, 40 lb bags
0.9 m³ is about 31.7 ft³; with a 10% allowance, 34.9 ft³. A 40 lb bag yields a typical 0.30 ft³, so 34.9 ÷ 0.30 = 116.3 → 117 bags. Big bag counts are the moment most people start comparing against a ready-mix truck.
Bags or ready-mix?
Around one cubic yard — roughly 45 of the 80 lb bags — is where most DIY budgets and backs start looking at a truck. Below that, bags win on convenience: no minimum order, no delivery window, and you can spread the work across a weekend. The concrete cost calculator puts your own prices on both options and shows where the line sits for your project.
Why yields differ
Bag yields look standard, but they are approximate. The yield depends on the size of the stone in the mix, how the bag was filled, and even how much it got shaken up in transit. The numbers here are typical examples; the yield printed on your bag is the one to trust, and the yield field is editable for that reason. If you are halfway through a job and your count came up short, the usual suspects are spillage, an uneven subgrade that ate more mix than expected, and bags packed less generously than the label.
Knowledge base
Frequently Asked Questions
How many 80 lb bags make one cubic yard?
One cubic yard is 27 ft³, and an 80 lb bag typically yields 0.6 ft³, so 27 ÷ 0.6 = 45 bags. That is the arithmetic behind the common advice that about a yard is where bag mixing stops being fun.
How much does an 80 lb bag of concrete yield?
Around 0.6 ft³ is a typical example, and 60 lb bags sit near 0.45 ft³. The yield printed on the bag you buy is the number to use — the field here is editable so you can match it.
Should I add extra bags beyond the count?
The allowance field does that for you: 5 to 10% extra is a common example for spillage, uneven ground and bags that yield a little less than expected. The count is always rounded up, never down.
At what volume should I switch from bags to a truck?
It depends on your local prices and how much mixing you want to do. As a scale example, a cubic yard is around 45 of the 80 lb bags. Enter your quotes in the concrete cost calculator and it will show the break-even volume for your project.
Are all concrete bags the same mix?
No — bags differ in the size of aggregate, intended use and working time, and each bag spells its own details out on the label. Pick a mix suited to your job and use the labeled yield in this calculator.
Do you store the numbers I enter?
No. The calculator runs entirely in your browser; nothing you type is stored or sent anywhere.
This calculator is an estimating tool for planning only. Quantities depend on site conditions, wastage and suppliers, and are not a quotation. Thickness, footing depth, reinforcement and mix strength must come from your plans, an engineer or your local building authority.
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