How many 60-lb or 40-lb bags make a cubic yard?
A cubic yard is 27 cu ft. A 60-lb bag yields 0.45 cu ft, so it takes 60 bags, and a 40-lb bag yields 0.30 cu ft, so it takes 90 bags. With 80-lb bags it is 45.
Concrete Bag Calculator: 80-lb, 60-lb and 40-lb Sacks
Find out how many bags of premixed concrete your project takes. The calculator converts the volume into 80-lb, 60-lb and 40-lb bags, shows the pallets and the weight you will have to carry, and compares the total with a ready-mix delivery.
1. Material Grade & Project Dimensions
Area: 80.0 sq ft (7.43 m²)Net Vol: 0.99 cu yd (0.76 m³)
2. Material Takeoff, Blueprint & Cost
Total Concrete Volume (incl. waste)
1.09 cu yd (0.83 m³)
29.3 cu ft · 4,341 lbs (2.17 US tons)
80-lb Concrete Bags (0.60 ft³)
49 bags
1.2 pallets (@ 42 bags/pallet)
60-lb or 40-lb Bag Option
66 × 60-lb
or 98 × 40-lb (0.30 cu ft)
Rebar Grid (#4 @ 18" O.C.)
116 lin ft
6 × 20-ft bars recommended
4" Compacted Gravel Sub-Base
1.40 US tons
Crushed stone base under slab
Cost Break-Even: Ready-Mix Truck vs. 80-lb Bags
Ready-Mix Truck saves $52
Ready-Mix Delivery (1.09 cu yd + $140 short-load fee)
$192
49 × 80-lb Pre-Mix Bags
$244
Show Step-by-Step Formula & Takeoff Math
Net Area = 80.00 sq ft (7.43 m²)
Net Volume = 26.67 cu ft ÷ 27 = 0.99 cu yd
Total Volume (+10% waste) = 29.33 cu ft = 1.09 cu yd (0.83 m³)
80-lb Bags = ceil(29.33 ÷ 0.60) = 49 bags
How many bags of concrete you need
The calculator assumes about 0.0075 cu ft of concrete per pound of dry mix. That makes an 80-lb bag yield 0.60 cu ft, a 60-lb bag 0.45 cu ft and a 40-lb bag 0.30 cu ft, so one cubic yard (27 cu ft) takes 45 bags of 80 lb, 60 bags of 60 lb or 90 bags of 40 lb. Check the yield printed on your brand of bag, because it can differ slightly.
Example: an 8×10 ft pad at 4 in is 26.7 cu ft, or 29.3 cu ft with a 10% allowance. That is 49 bags of 80-lb, 66 bags of 60-lb or 98 bags of 40-lb mix. The 80-lb option is 1.2 pallets at 42 bags per pallet.
Bags are heavy to move: 49 bags of 80 lb weigh 3,920 lb, close to 2.0 US tons, before any water is added. If you need more than about 50 bags the calculator shows a ready-mix delivery as the cheaper route at its default prices ($6.45 per 80-lb bag, $165 per cu yd).
Bags of concrete for common small projects (4 in thick)
| Project | Size | 80-lb bags | 60-lb bags | 40-lb bags |
|---|---|---|---|---|
| Small landing | 4×4 ft | 10 | 14 | 20 |
| Step or stoop pad | 4×6 ft | 15 | 20 | 30 |
| Equipment pad | 6×8 ft | 30 | 40 | 59 |
| Shed base | 8×10 ft | 49 | 66 | 98 |
| Shed floor | 10×10 ft | 62 | 82 | 123 |
| Larger slab | 10×12 ft | 74 | 98 | 147 |
Frequently Asked Questions & Field Guide
How many bags of concrete do I need for a 4x4 slab?
A 4×4 ft slab at 4 in is 5.33 cu ft, or 5.87 cu ft with the 10% allowance. That takes 10 bags of 80-lb, 14 bags of 60-lb or 20 bags of 40-lb mix.
How much do the bags weigh in total?
Multiply the bag count by the bag weight. For the 8×10 ft pad above, 49 bags of 80 lb weigh 3,920 lb as dry mix. The same job with 40-lb bags needs 98 bags, about 3,920 lb, which is easier to lift but means more bags to open and mix.
When should I switch from bags to ready-mix?
At the default prices the calculator finds ready-mix cheaper from about 1.1 cu yd, or 50 bags of 80 lb. The exact break-even depends on the bag price and on the delivery fee in your area, so enter your own prices and read the comparison box. The slab cost calculator explains the comparison in more detail.
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