How to use the concrete bag calculator calculator
- 1
Pick where you are starting from
Use area and thickness if you are measuring a pour, known cubic feet if you have already worked out the volume, or known cubic yards if you are converting a ready-mix figure into bags.
- 2
Enter the volume or the measurements
For the area mode, enter the square footage and the thickness with its unit. For the volume modes, enter the cubic feet or cubic yards directly. Cubic yards are converted at exactly 27 cubic feet per yard.
- 3
Read the yield off the bag
Find the yield on the bag label or in the manufacturer documentation, stated as the cubic feet of finished concrete one bag makes, and enter it. Do not use a remembered figure: yields differ by product and by bag weight.
- 4
Add an allowance if you want one
An optional percentage covers spillage, an uneven base, and the material left in the mixer. Bags make this easy to absorb, since buying one or two spare is cheap compared with stopping a pour.
- 5
Add your price for a cost estimate
Enter the shelf price per bag, and any delivery or fixed fee, to see the estimated total alongside the bag count.
Formula
Bags = cubic feet required / bag yield in cubic feet
Round the result up. To find bags per cubic yard, divide 27 by the yield instead.
Worked example
A 4 ft x 4 ft equipment pad at 4 inches, using a bag with a stated 0.45 cubic foot yield
- 1Find the area: 4 ft x 4 ft = 16 square feet.
- 2Convert the thickness: 4 in / 12 = 0.3333 ft.
- 3Find the volume: 16 x 0.3333 = 5.33 cubic feet.
- 4Divide by the yield entered: 5.33 / 0.45 = 11.85 bags.
- 5Round up: 12 bags.
The pad takes 12 bags at that yield. The 0.45 figure is the yield entered for this example, not product data.
Worked examples
From a known cubic yard figure
Converting one cubic yard into bags at a 0.6 cubic foot yield
- 1Convert the volume: 1 cubic yard = 27 cubic feet.
- 2Divide by the yield: 27 / 0.6 = 45 bags.
- 3No rounding is needed here because the division is exact.
One cubic yard takes 45 bags at a 0.6 cubic foot yield. At a 0.45 yield the same cubic yard takes 60 bags, which shows how much the yield matters.
Bag cost from your own price
A 20 ft x 3 ft walkway at 4 inches, with a 0.5 cubic foot yield and a $6.50 shelf price
- 1Area: 20 x 3 = 60 square feet.
- 2Volume: 60 x 0.3333 = 20 cubic feet.
- 3Bags: 20 / 0.5 = 40 bags exactly.
- 4Cost: 40 x $6.50 = $260.
The walkway takes 40 bags for an estimated $260 in material. Both the yield and the price are figures entered for this example.
Why bag yield matters more than bag weight
Concrete mix is sold by weight but used by volume, and the two do not track each other in a way you can guess. Two bags of the same weight can produce different volumes of finished concrete, because the aggregate, the cement content, and the water added all differ between products.
That is why every bag prints a yield: the cubic feet of finished concrete one bag makes when mixed as directed. The yield, not the weight, is the number that converts your volume into a bag count. Working from weight alone will not give you a reliable answer.
The practical effect is large. A pour needing 27 cubic feet takes 45 bags at a 0.6 cubic foot yield and 60 bags at a 0.45 yield. That is a third more bags for the same pour, which is why YardCalc asks you to enter the yield rather than assuming one on your behalf.
How to read a concrete bag label
The yield is usually printed near the mixing instructions. Look for these things:
- 1Find the stated yield, given as cubic feet of finished concrete per bag. Some labels give it per bag; others state it for a stack of bags, so check which.
- 2Note the bag weight the yield applies to. The same product in a heavier bag has a proportionally larger yield, and labels sometimes list several.
- 3Check the mixing water quantity. The stated yield assumes the bag is mixed as directed, so adding extra water changes the material rather than stretching the yield usefully.
- 4Note the product type. Different mixes are formulated for different uses, and choosing between them is a specification matter rather than a calculation.
- 5Enter the yield exactly as printed. If the label gives a range, using the lower end is the conservative choice for ordering.
Rounding up, and how much spare to buy
The division almost never lands on a whole number, and you cannot buy part of a bag, so the count always rounds up. The calculator shows the exact figure as well, because it tells you how close you are to the next bag: a result of 11.05 bags means you are barely into the twelfth, while 11.9 means the twelfth is nearly full.
Beyond rounding, most people buy a little spare. Some material is lost to the mixer, to spillage, and to a base that is slightly lower in places than it looked. Bags are easy to keep dry and return or store, so the cost of one or two extra is usually small next to the cost of stopping partway through a pour.
How much spare is a judgment call that depends on your site and your tolerance for a second trip, so the calculator offers an allowance field rather than applying a figure of its own.
Common mistakes
The usual reasons a bag count comes out wrong:
- Using a yield from memory or from a different product instead of the one printed on the bag being bought.
- Confusing bag weight with bag yield, and dividing by the weight.
- Forgetting to convert cubic yards to cubic feet before dividing, which understates the count by a factor of 27.
- Rounding down, or rounding to the nearest bag rather than up.
- Buying exactly the calculated count with no spare on a pour that cannot be paused.
- Applying a yield stated for a stack of bags as if it were the yield of one bag.
Bag-yield math: bags per cubic yard
Mathematical bag-yield examples showing 27 cubic feet divided by each yield. These are round numbers chosen to demonstrate the arithmetic, not product data. Use the yield printed on the actual concrete bag or supplier documentation.
| Bag volume | Bags per cubic yard | Whole bags for 1 cubic yard |
|---|---|---|
| 0.33 cu ft | 81.82 | 82 |
| 0.45 cu ft | 60 | 60 |
| 0.6 cu ft | 45 | 45 |
| 0.75 cu ft | 36 | 36 |
| 1 cu ft | 27 | 27 |
Bag-yield math: whole bags by project size
Whole bags required for a given project volume at each example yield, rounded up. Again these yields are arithmetic examples only.
| Bag volume | 0.25 yd | 0.5 yd | 1 yd | 2 yd | 3 yd | 5 yd |
|---|---|---|---|---|---|---|
| 0.33 cu ft | 21 | 41 | 82 | 164 | 246 | 410 |
| 0.45 cu ft | 15 | 30 | 60 | 120 | 180 | 300 |
| 0.6 cu ft | 12 | 23 | 45 | 90 | 135 | 225 |
| 0.75 cu ft | 9 | 18 | 36 | 72 | 108 | 180 |
| 1 cu ft | 7 | 14 | 27 | 54 | 81 | 135 |
Frequently asked questions
- How many bags of concrete do I need for 1 cubic yard?
- Divide 27 cubic feet by the yield printed on the bag. At a 0.6 cubic foot yield that is 45 bags, at 0.45 it is 60 bags, and at 0.33 it is 82 bags. Because yields differ by product and bag weight, use the figure on the bag you are buying.
- How many bags of concrete for a 10 x 10 slab?
- A 10 by 10 foot slab at 4 inches is 33.33 cubic feet. At a 0.6 cubic foot yield that is 56 bags, and at a 0.45 yield it is 75 bags. Enter your own yield above for the exact count.
- Is bag yield the same as bag weight?
- No. Weight is what you carry; yield is the volume of finished concrete the bag produces. Only the yield converts a volume into a bag count, and two bags of equal weight can have different yields.
- Should I round up or down?
- Always up. Partial bags are not sold, and finishing a pour short is far more costly than an unused bag. The calculator shows the exact figure too, so you can see how close the last bag is to being needed in full.
- Where do I find the yield on the bag?
- It is normally printed near the mixing instructions, given as cubic feet of finished concrete per bag. Check whether the figure is stated per bag or for a group of bags, and confirm which bag weight it applies to.
- Can I use this for post holes or footings?
- Yes, if you already know the volume. Calculate it with the post hole or footing calculator, then bring the cubic-foot figure here, or use the bag fields built into those tools directly.
Bag counts are the required volume in cubic feet divided by the bag yield you enter, rounded up to whole bags. YardCalc publishes no product-specific bag yields; the yields shown in tables are arithmetic examples. Concrete calculations estimate material quantity from geometry and user-entered values. Confirm mix design, thickness, reinforcement, code requirements, bag yield, delivery, and final order quantity with the appropriate supplier or professional.
Results are planning estimates. Last reviewed 2026-07-28.