Convert Cubic Feet to Concrete Bags
Use this Cubic Feet to Concrete Bags calculator to estimate how many bags of concrete mix are needed for a target volume. Choose 40, 50, 60 or 80 lb bags, add an optional waste allowance, and the calculator will round up to whole bags. Bag yields vary by product, so the tool uses common approximate yields and should be checked against the yield printed on your specific concrete mix.
Estimate bags from cubic feet, convert bags back to approximate concrete volume, calculate bags from slab dimensions, or compare all common bag sizes side by side.
Enter required concrete volume, choose bag size and add an optional overage percentage.
10% is a practical starting allowance; adjust for your project.
Estimate how much mixed concrete volume a chosen number of bags may produce.
Calculate cubic feet from slab length, width and thickness, then estimate whole concrete bags.
Enter cubic feet and compare estimated 40, 50, 60 and 80 lb bag quantities at once.
To convert cubic feet of concrete into bags, divide the required concrete volume by the approximate yield of one bag, then round up to the next whole bag. Because bagged concrete is sold as complete bags, a calculation of 12.2 bags means you normally need to buy 13 bags before adding any extra allowance.
Then apply any waste allowance and round up to the next whole bag.
For example, if you need 6 cubic feet and an 80 lb bag yields approximately 0.60 cubic foot, the base estimate is 6 ÷ 0.60 = 10 bags. With a 10% allowance, the adjusted volume becomes 6.6 cubic feet, or 11 bags at the same assumed yield.
Find project volume in cubic feet before estimating bag quantity.
Different bag weights produce different approximate concrete yields.
Bag quantities should normally be rounded up to whole bags.
Extra material helps cover uneven subgrade, spillage and estimating differences.
The following figures are practical approximate yields for standard bagged concrete mix. Manufacturer data confirms that yields vary by product, so use the specific bag label for final purchasing.
| Bag Size | Approx. Yield per Bag | Bags per 1 ft³ | Approx. Bags per 1 yd³ |
|---|---|---|---|
| 40 lb | 0.30 ft³ | 3.34 bags | 90 bags |
| 50 lb | 0.38 ft³ | 2.64 bags | 72 bags |
| 60 lb | 0.45 ft³ | 2.23 bags | 60 bags |
| 80 lb | 0.60 ft³ | 1.67 bags | 45 bags |
QUIKRETE lists approximately 0.45 ft³ for a 60 lb bag and 0.60 ft³ for an 80 lb bag of its standard Concrete Mix. Sakrete lists approximately 0.30, 0.45 and 0.60 ft³ for 40, 60 and 80 lb High-Strength Concrete Mix bags, and its slab guidance cites approximately 0.38 ft³ for a 50 lb bag. See QUIKRETE Concrete Mix data and Sakrete High-Strength Concrete Mix.
3 ÷ 0.60 = 5 bags before extra allowance.
6 ÷ 0.45 = 13.33, so round up to 14 bags.
10 ÷ 0.38 = 26.32, so round up to 27 bags.
12 ÷ 0.30 = 40 bags before extra allowance.
A bag weight tells you the mass of dry concrete mix, but the useful project quantity is the volume of mixed and placed concrete. Yield can vary by product formulation, aggregate grading, water addition and manufacturer specifications. That is why a simple pounds-to-cubic-feet conversion is not appropriate for bagged concrete.
The safest workflow is to calculate project volume, read the stated yield on the exact bag you intend to buy, divide required volume by that yield, add your chosen allowance and round up. Manufacturer calculators also note that their yields are approximate and do not automatically cover uneven subgrade or waste.
An overage allowance can help account for subgrade variation, forms that are not perfectly uniform, spillage, small measurement errors and concrete left in mixing equipment. Sakrete's current concrete calculator guidance recommends adding 10% to estimates as a safety margin, which is why this calculator starts at 10% but lets you change the value.
The right allowance depends on the project. A carefully measured, formed slab on a uniform base may need less extra than an irregular excavation or post-hole project. The calculator treats the percentage as an adjustable estimating input, not a universal requirement.
Measure the project volume, divide by the chosen bag yield, add allowance if needed, then round up.
For a rectangular slab, multiply length in feet by width in feet by thickness in feet. If thickness is measured in inches, divide the thickness by 12 before multiplying. A 10 ft × 8 ft slab at 4 inches thick has a volume of 10 × 8 × (4 ÷ 12) = 26.67 cubic feet.
After finding cubic feet, divide by the bag yield and round up.
The slab calculator above performs both steps. For irregular shapes, divide the project into simpler rectangles or other measurable sections, calculate each volume separately and add the totals before converting cubic feet to bags.
One cubic yard contains exactly 27 cubic feet. Using approximate standard yields, a cubic yard takes about 45 bags of 80 lb mix, 60 bags of 60 lb mix, about 72 bags of 50 lb mix or 90 bags of 40 lb mix before extra allowance. Sakrete specifically notes that 45 standard 80 lb bags are about one cubic yard.
For larger pours, compare the cost, labor and handling of dozens of bags with ready-mix delivery. Bagged concrete is convenient for smaller slabs, repairs, steps and post settings, but the most practical supply method depends on project size and site access.
Pounds measure mass; cubic feet measure volume. Use the manufacturer's stated mixed-concrete yield.
You generally cannot purchase a fraction of a bag, so round the final quantity upward.
For slab thickness, divide inches by 12 before calculating cubic feet.
Real pours often require more material than ideal geometric volume.
Products with the same bag weight can have different formulations and yields.
Larger bags generally cover more cubic feet per bag, so fewer bags are required for the same project volume. However, bag weight also affects handling. An 80 lb bag may reduce the total bag count but is heavier to lift and mix. Smaller bags can be easier to move in tight spaces or for small repairs.
The comparison calculator above shows how bag count changes for the same adjusted project volume. It does not compare price, labor or product strength because those factors depend on the specific concrete mix and retailer.
For related estimating tasks, use the Concrete Bags to Cubic Feet calculator, Concrete Bags to Cubic Yards calculator, Square Concrete Calculator, Gravel Calculator for Concrete, or Liters to Cubic Meters converter. Keeping project dimensions, volume and bag yield separate makes concrete quantity estimates easier to check.
Quick answers about bag yield, cubic feet, slab volume, concrete bag sizes and extra material.