Concrete bag calculator
How many bags of concrete mix to buy for a slab, pad or footing. The result shows every bag size side by side, using the yields printed on the manufacturer’s data sheet, and rounds up to whole bags.
Calculator
Bags to buy
Enter your measurements and select Calculate bags.
- Bags of 80 lb mix
- Volume with waste
- cu ft
- Exact volume
- cu ft / cu yd
- Cost with bags
- Ready-mix instead
- cu yd,
- Best way to buy
| Bag | Yield | Bags |
|---|
Bags = volume with waste in cubic feet ÷ yield of one bag, rounded up.
How the bag calculator works
Bagged concrete mix is sold by dry weight, but what you need is wet volume. Each manufacturer publishes a yield: the cubic feet of placed concrete one bag makes. The calculator works out the volume of your pour, adds the waste allowance, then divides by the yield and rounds up to a whole bag.
Bags = (length × width × thickness ÷ 12) × (1 + waste %) ÷ yield per bag, rounded up
Bag yields used
| Bag | Yield | Bags per cu yd | Bags per cu ft |
|---|---|---|---|
| 40 lb | 0.30 cu ft | 90 | 3.33 |
| 50 lb | 0.375 cu ft | 72 | 2.67 |
| 60 lb | 0.45 cu ft | 60 | 2.22 |
| 80 lb | 0.60 cu ft | 45 | 1.67 |
| 90 lb | 0.675 cu ft | 40 | 1.48 |
Source: QUIKRETE Concrete Mix data sheet, product 1101. Sakrete’s standard 80 lb mix is listed by distributors at the same 0.60 cu ft. High-yield products such as Sakrete MAXIMIZER yield more per bag, so check the label of the product you buy.
Worked example
A shed base 8 ft by 10 ft at 4 in thick:
- Volume: 8 × 10 × (4 ÷ 12) = 26.67 cu ft
- With 10% waste: 26.67 × 1.10 = 29.33 cu ft
- 80 lb bags: 29.33 ÷ 0.60 = 48.9, so buy 49 bags
- 60 lb bags: 29.33 ÷ 0.45 = 65.2, so buy 66 bags
That is just under one cubic yard. Forty-nine bags is a full day for one person with a mixer, so it is worth pricing a short ready-mix load too.
Which bag size to buy
- 80 lb bags give the lowest cost per cubic foot at most stores and need the fewest trips, but each one weighs 80 lb to lift and mix. Use the water quantity printed on the bag.
- 60 lb bags are easier to lift and fit a small mixer better.
- 40 and 50 lb bags suit repairs, post setting and small pads.
- 90 lb bags are sold in some regions only.
Enter your store’s price per bag to see the total. For a fair comparison with a truck, enter your plant’s price per cubic yard too.
Limitations
- Yields are the manufacturer’s approximate figures and exclude spillage and uneven ground. Keep the waste allowance.
- Mixing with too much water increases volume slightly and weakens the concrete. Follow the bag’s water instructions.
- Yields differ between brands and products. Fast-setting, high-strength and high-yield mixes have their own figures.
- For round holes, use the column option on the main calculator and read the bag count there.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
45 bags. One cubic yard is 27 cubic feet, and an 80 lb bag yields 0.60 cubic feet, so 27 ÷ 0.60 = 45.
How many 60 lb bags of concrete make a yard?
60 bags. 27 cubic feet ÷ 0.45 cubic feet per bag = 60.
How much does an 80 lb bag of concrete cover?
An 80 lb bag yields 0.60 cubic feet, which covers 1.8 square feet at 4 inches thick, or 3.6 square feet at 2 inches thick.
Is it cheaper to buy bags or ready-mix?
Bags usually cost more per cubic yard than ready-mix but have no delivery or minimum-load fees. For small jobs under about a cubic yard, bags typically win. For larger pours, a truck usually costs less and saves a day of mixing. Use the cost calculator with your local prices.
Sources
- QUIKRETE Concrete Mix Data Sheet, Product No. 1101, revised October 2022, yield per bag. quikrete.com