How it works
The calculator adds your extra allowance to the volume and divides by the yield of one bag.
Volume incl. extra = Volume × (1 + Extra ÷ 100)
Bags = ⌈ Volume incl. extra ÷ Yield per bag ⌉
Total bag weight = Bags × Bag weight
⌈ ⌉ means rounding up to the next whole bag. Rounding happens only at the end.
The yield is the key number: it is the volume of mixed concrete one bag produces, and it is printed on the bag. Bag weight on its own doesn’t tell you the volume. This tool estimates material quantity only; it does not assess whether a mix or a design is suitable.
Worked example
Inputs
- Concrete volume needed
- 10 cu ft
- Yield per bag
- 0.6 cu ft
- Bag weight
- 80 lb
- Extra concrete
- 10 %
Result
- Bags
- 19
- Volume incl. extra
- 11 cu ft (0.407 cu yd)
- Total bag weight
- 1,520 lb (0.76 short tons)
Common mistakes
- Assuming all bags of the same weight make the same volume. Different mixes and brands can yield different volumes – read the bag.
- Entering the slab volume in cubic yards while the yield is in cubic feet without checking the unit menus. The calculator converts units, but only if each field shows the right one.
- Buying exactly the calculated number of bags. Running out halfway through a pour is worse than returning an unopened bag.
- Forgetting the weight. A few dozen bags can exceed what a car or a light trailer can carry safely; check your vehicle’s payload.
Assumptions and limits
- The yield you enter is the mixed volume per bag stated by the manufacturer. Real yield varies a little with water content and compaction.
- Bags are rounded up to whole bags after the extra allowance is added.
- Total weight is bag count × bag weight, the dry weight of the bags you carry, not the weight of the placed concrete.
- The result is a material quantity only, not a structural design.
Frequently asked questions
How much concrete does one bag make?
Check the bag. As one example, QUIKRETE’s data sheet for its Concrete Mix (No. 1101) lists about 0.30 cu ft for a 40 lb bag, 0.45 cu ft for 60 lb, 0.60 cu ft for 80 lb and 0.675 cu ft for 90 lb. Other products and brands can differ.
How many bags make a cubic yard?
Divide 27 cubic feet by the yield of your bag and round up. With a bag that yields 0.60 cu ft, that is 27 ÷ 0.60 = 45 bags before any extra; with 0.45 cu ft it is 60 bags.
Is it better to buy bags or order ready-mix?
For small jobs, bags are often simpler; for larger pours, mixing many bags by hand takes time and the concrete has to be placed before earlier batches set. Compare the bag count and weight here with a ready-mix quote for your volume.
My bag label gives the yield in liters. Can I enter that?
Yes. Switch to metric units and enter the yield in liters as printed, or keep US units and convert – one cubic foot is about 28.3 liters.
Sources
- QUIKRETE Concrete Mix (No. 1101) Product Data Sheet — The QUIKRETE Companies. Yield per bag: 40 lb ≈ 0.30 ft³, 50 lb ≈ 0.375 ft³, 60 lb ≈ 0.45 ft³, 80 lb ≈ 0.60 ft³, 90 lb ≈ 0.675 ft³.
- NIST Handbook 44, Appendix C – General Tables of Units of Measurement — National Institute of Standards and Technology. Exact unit definitions: 1 in = 2.54 cm, 1 yd³ = 27 ft³, 1 US gal = 231 in³, 1 lb = 0.45359237 kg.
Method reviewed November 2, 2026