Concrete Bag Calculator
0 bags · 80 lb
Enter a slab or post hole size in the concrete bag calculator, or a volume you already know, and see how many bags of concrete you need: 80, 60, 50 or 40 lb. Bags = cubic feet ÷ the yield of one bag, rounded up. Quikrete lists 0.60 ft³ for an 80 lb bag, so a cubic yard (27 ft³) takes 45 bags.
In this concrete calculator, bags come in all four sizes at once. The line under the big number reads 40 lb 112 · 50 lb 89 · 60 lb 75 · 80 lb 56 for a 10' × 10' × 4" slab, so you can match it to whatever is on the shelf. Already have the volume from a plan? Switch to Volume and type it in yd³, ft³ or m³. No need to enter the sizes again.
A bag, or sack, of mix is sold by weight, but the form fills by volume. That's why the count changes with the size you carry.
How many bags of concrete do I need?
Get the volume in cubic feet, then divide by the yield of one bag. For a slab:
length (ft) × width (ft) × thickness (in) ÷ 12 = cubic feet
cubic feet ÷ yield per bag = bags, rounded up
Take a 10' × 10' × 4" slab. 10 × 10 × 4 ÷ 12 = 33.33 ft³, which is 1.23 yd³. Then 33.33 ÷ 0.60 = 55.6, so 56 bags of 80 lb. The other sizes: 75 of 60 lb, 89 of 50 lb, 112 of 40 lb.
Starting from square feet? Multiply by thickness (in) and divide by 12. The same slab is 100 ft², and at 4" it's the same 33.33 ft³.
We add 10% by default, because a short pour costs more than a few spare bags. With 10%, the slab is 36.67 ft³: 62 bags of 80 lb, 82 of 60 lb, 98 of 50 lb, 123 of 40 lb. Set Extra % anywhere from 0 to 50; 0 means no extra. The result is labeled incl. 10% extra.
A bags of concrete calculator does this division for you, and the steps above let you check it. The part a concrete calculator by the bag has to get right is rounding: once, on the total, and always up to a whole bag.
80 lb, 60 lb, 50 lb and 40 lb bags
Tap a size in the line under the result. It becomes the big number and the size that goes to your project. So the same tool is an 80 lb bag of concrete calculator, a 60 lb bag concrete calculator or a 50 lb bag concrete calculator, depending on what you tap.
Prices differ by size, so Price sits under the line and keeps a separate price for each one: Price per 80 lb bag, Price per 60 lb bag and so on. Enter yours and the result shows Cost $… for the selected size. No price, no cost line.
The 80 lb on the bag is the weight of the dry mix, not of the concrete once it's poured. For poured weight in pounds or tons, check the weight of concrete for your volume.
Switch to metric for 25 kg and 20 kg bags. Their yield is an estimate, worked out from Quikrete's yield per kilogram: about 0.0117 m³ for 25 kg and 0.0094 m³ for 20 kg.
How many cubic feet in a bag of concrete
It depends on the bag. Quikrete lists 0.60 ft³ for an 80 lb bag, 0.45 for 60 lb, 0.375 for 50 lb and 0.30 for 40 lb. Those are the numbers the calculator divides by.
At 4" thick, one bag covers its yield ÷ (4 ÷ 12):
| Bag | Yield (ft³) | Covers at 4" (ft²) |
|---|---|---|
| 80 lb | 0.60 | 1.8 |
| 60 lb | 0.45 | 1.35 |
| 50 lb | 0.375 | 1.125 |
| 40 lb | 0.30 | 0.9 |
How many bags of concrete in a yard
A cubic yard is 27 ft³. Divide 27 by the yield:
| Bag | Bags per yd³ |
|---|---|
| 80 lb | 45 |
| 60 lb | 60 |
| 50 lb | 72 |
| 40 lb | 90 |
With 10% extra, a yard of 80 lb bags is 50: 49.5, rounded up.
Bags for a slab, footing or post hole
Slab handles a slab, a patio or a walk. Used as a concrete bag calculator for slab pours, it takes length, width and thickness in inches, plus Quantity for several slabs of one size. Typical sizes and thickness tips are on the concrete slab calculator.
For a footing, use Slab: it's the same rectangle. Enter the length of the run and the width, and put the depth in Thickness. That makes Slab the concrete bag calculator for footing work too. The project line reads Slab 20' × 2'; tap the name to rename it. Walls, columns and steps have their own tabs on the concrete calculator, which counts bags as well.
Round covers a sonotube, a column or a post hole. Enter the diameter (in), the depth and the quantity. Got twelve tubes of one size? Enter one and set Quantity to 12. That turns Round into a sonotube concrete bag calculator, with no adding by hand.
Bags of concrete for a fence post
To work out how many bags of concrete for a fence post, use Round: hole diameter, hole depth, and the post in Post diameter. The post is subtracted from the hole.
Example: a Ø10" hole 36" deep with a Ø4" post comes to 1.37 ft³. That's 3 bags of 80 lb, 4 of 60 lb, 4 of 50 lb or 5 of 40 lb. With 10% extra it's 1.51 ft³: 3, 4, 5 or 6.
A whole fence of 12 such holes is 16.49 ft³ (0.61 yd³): 28 bags of 80 lb, 37 of 60 lb, 44 of 50 lb, 55 of 40 lb. With 10%, 18.14 ft³ and 31 bags of 80 lb. Bags are rounded on the total, not per hole, since mix left over from one hole goes into the next. Rounded hole by hole, the same fence would take 36.
Square 4x4 post? It measures 3.5" × 3.5", so enter 3.5 in Post diameter. A round post that wide is a little smaller than the square one, and the count comes out slightly high. That's the safe side.
Hole size and depth come from your plans or local code. This page gives the bags.
Bags or ready-mix?
Bagged concrete is mixed on site, one bag at a time. Quikrete lists about 6 pt of water per 80 lb bag. Ready-mix arrives by truck and is sold by the cubic yard.
This page counts bags. For yards of ready-mix, use the concrete calculator: same shapes, result in yd³. Whether a truck makes sense at your size depends on your plant, so ask about its minimum order and delivery terms.
What's next
Press Add to project under the result. The size you picked goes to My project as a line, for example Slab 10' × 10' with 56 bags 80 lb, or 1.5 yd³ volume if you started from a volume. Tap the name to rename it. Lines from the other construction calculators sit in the same list, with a total per material at the bottom, and you can print it. The numbers you enter stay in your browser; no account needed.
FAQ
How many 80 lb bags of concrete do I need?
Divide the volume in cubic feet by 0.60, Quikrete's yield for an 80 lb bag, and round up. A 10' × 10' × 4" slab needs 56, or 62 with 10% extra. For any other shape, the tool above works as an 80 lb bag of concrete calculator: tap 80 lb in the line under the result.
How much does a 60 lb bag of concrete cover?
1.35 ft² at 4" thick. Quikrete lists 0.45 ft³ for a 60 lb bag, and 0.45 ÷ (4 ÷ 12) = 1.35.
How many cubic feet will a 50 lb bag of concrete cover?
0.375 ft³, according to Quikrete. Poured 4" thick, that's 1.125 ft².
How many bags of concrete do I need for a 4x8 slab?
At 4" thick, a 4' × 8' slab is 10.67 ft³: 18 bags of 80 lb, 24 of 60 lb, 29 of 50 lb or 36 of 40 lb. With 10% extra, it's 20, 27, 32 or 40.
How many 80 lb bags of concrete in a yard?
- A yard is 27 ft³, and 27 ÷ 0.60 = 45 at Quikrete's yield per 80 lb bag. With 10% extra it's 50. Three yards take 135 bags, or 149 with 10%.
Results are estimates for ordering material. Check the quantity with your supplier before you order.