Concrete Bag Calculator
A 12 ft by 24 ft slab, 4 inches thick, takes 160 bags of 80 lb premix. The same pour is 214 bags at 60 lb and 320 bags at 40 lb.
Last updated . The 80 lb yield is 0.60 ft³ and the 60 lb yield is 0.45 ft³, the figures already stated on the concrete calculator. Waste starts at 0%.
Turn a length, width, and thickness into a bag count for 40, 60, and 80 lb premix, or for 25 and 50 kg bags scaled from the 80 lb yield. The count rounds up. Edit the yield when the bag in your hand prints a different number.
Volume and weight for this pour are on the concrete calculator. Bags of cement, rather than premix, are on the cement calculator. When the pour might be a truck instead of sacks, read bags versus ready-mix.
Concrete bags
Results
How the bag count is calculated
The 12 ft × 24 ft × 4 in pour is 96.00 ft³. One cubic foot is 0.028316846592 m³, so the same box is 2.7184 m³, which rounds to 2.72 m³. Divided by 27 it is 3.56 cubic yards. Those are the volume figures on the concrete calculator for this slab. This page does not weigh the pour. At 2,400 kg/m³ that other page reads 7.19 short tons and 6.52 tonnes.
An 80 lb bag yields 0.60 ft³, so 96.00 ÷ 0.60 = 160 bags. A 60 lb bag yields 0.45 ft³, so 96.00 ÷ 0.45 = 213.33, and the order rounds up to 214. A 40 lb yield of 0.30 ft³ is half of the 80 lb yield. Check the bag. 96.00 ÷ 0.30 = 320. The concrete calculator’s 192 is a count of 0.5 ft³ units, not a count of 80 lb bags.
For kilogram bags, 80 × 0.45359237 = 36.287 kg, and 0.60 × 0.028316846592 = 0.01699 m³. A 25 kg bag is 25 ÷ 36.287 × 0.01699 m³ = 0.01171 m³. A 50 kg bag is twice that, 0.02341 m³. The tool divides the full 2.7184 m³ by those yields and rounds up: 233 bags at 25 kg, and 117 bags at 50 kg. That scale is a planning yield, not a product printed on a 25 kg sack.
Worked example
Leave the length at 12 ft, the width at 24 ft, the thickness at 4 in, the bag on 80 lb, and the waste at 0. Volume reads 3.56 yd³, 96.00 ft³, and 2.72 m³. Bags reads 160. Per cubic yard reads 45.00. The line under the results is 96.00 ft³ ÷ 0.60 ft³ = 160.00, rounded up to 160 bags.
Frequently asked questions
How many 80 lb bags of concrete do I need for a 12 by 24 foot slab?
Leave the size at 12 ft by 24 ft by 4 inches and the bag on 80 lb. The volume is 3.56 cubic yards, 96.00 cubic feet, and 2.72 cubic meters, the same pour as the concrete calculator. An 80 lb bag yields 0.60 cubic feet on that page. 96.00 ÷ 0.60 = 160.00, so the order is 160 bags. That is 45.00 bags per cubic yard.
How many 60 lb and 40 lb bags is that slab?
Switch the bag menu. A 60 lb bag yields 0.45 cubic feet, the figure already on the concrete calculator. 96.00 ÷ 0.45 = 213.33, which rounds up to 214 bags, 60.00 bags per cubic yard. A 40 lb yield of 0.30 cubic feet is half of the 80 lb yield. Check the bag. 96.00 ÷ 0.30 = 320 bags, 90.00 per cubic yard.
How many 25 kg and 50 kg bags is the same slab?
80 lb is 36.287 kg, and 0.60 cubic feet is 0.01699 cubic meters. Scaling that yield by mass gives 0.01171 cubic meters for 25 kg and 0.02341 cubic meters for 50 kg. Those are not a quoted brand. The full slab volume is 2.7184 cubic meters. Divided by 0.01171 it is 232.14, which rounds up to 233 bags of 25 kg. Divided by 0.02341 it is 116.12, which rounds up to 117 bags of 50 kg.
Why does the concrete calculator show 192 bags?
The concrete calculator’s order line counts 0.5 cubic foot units. For this 12 by 24 foot slab that line is 192. The same page says not to take 192 bags of 80 lb mix to the store, and it already gives 160 bags at 0.60 cubic feet and 214 bags at 0.45 cubic feet. This page is those bag yields. The 192 figure is not repeated here as an 80 lb count.
Is this the same as the cement calculator?
No. The cement calculator counts bags of cement in a mix of cement, sand, and aggregate. This page counts bags of premixed concrete. An 80 lb bag here yields 0.60 cubic feet of concrete. A bag of portland cement does not yield that. Use the cement calculator when the ticket is cement, and this page when the ticket is premix.
How do I add 10 percent for waste?
Type 10 in the waste box. The percent is added to the volume before the bags are counted. The 96.00 cubic feet become 105.60 cubic feet. 105.60 ÷ 0.60 = 176 bags of 80 lb mix. The same 10 percent on a 60 lb bag is 235 bags, because 105.60 ÷ 0.45 = 234.67 and that rounds up. At 0 percent the 80 lb count stays 160.
What if my bag prints a different yield?
Change the yield box. The bag menu only fills a starting yield. The 0.60 and 0.45 cubic foot figures are the ones already stated on the concrete calculator. The 0.30 cubic foot figure for 40 lb is half of 0.60, and it should be checked against the bag. The kilogram yields are a mass scale of the 80 lb yield, using 0.45359237 kg per pound and 0.028316846592 cubic meters per cubic foot. Weight of the pour, at 2,400 kg/m³, stays on the concrete calculator: 7.19 short tons and 6.52 tonnes for this slab.