How Many Cubic Feet in a Bag of Concrete?
An 80 lb bag of concrete mix yields about 0.6 cubic feet of mixed concrete. A 60 lb bag yields 0.45 ft³, a 50 lb bag 0.375 ft³, and a 40 lb bag 0.3 ft³.
The rule of thumb: yield in cubic feet is roughly the bag weight divided by 133.
| Bag size | Cubic feet | Cubic yards | Litres |
|---|---|---|---|
| 40 lb | 0.30 ft³ | 0.011 yd³ | 8.5 L |
| 50 lb | 0.375 ft³ | 0.014 yd³ | 10.6 L |
| 60 lb | 0.45 ft³ | 0.017 yd³ | 12.7 L |
| 80 lb | 0.60 ft³ | 0.022 yd³ | 17.0 L |
| 90 lb | 0.675 ft³ | 0.025 yd³ | 19.1 L |
Standard pre-mixed concrete. Mortar, sand mix, and fast-setting products have different yields.
Why the yield is less than you'd guess
Dry mix is sand, gravel, and cement with air between the particles. Adding water fills that air space rather than expanding the volume, so 80 lb of dry material makes only about 0.6 cubic feet of finished concrete.
Cured concrete weighs roughly 150 lb per cubic foot, and 80 lb ÷ 0.6 ft³ = 133 lb per cubic foot of dry mix. The gap is the water you add.
Turning yield into a bag count
Get your volume in cubic feet, then divide by the yield. For a 6 ft × 3 ft landing at 4 inches:
- Volume: 6 × 3 × 0.333 = 6 ft³
- 80 lb bags: 6 ÷ 0.6 = 10 bags
- 60 lb bags: 6 ÷ 0.45 = 13.3 → 14 bags
The bags of concrete calculator does this for every bag size at once.
Yields for related products
Not every bag in the aisle is concrete mix, and the yields differ:
- Concrete mix (80 lb): 0.6 ft³ — sand, gravel, cement, for slabs and footings
- Fast-setting concrete (50 lb): about 0.375 ft³ — post holes, sets in 20–40 minutes
- Sand mix / topping (60 lb): about 0.5 ft³ — no coarse gravel, for thin overlays
- Mortar mix (80 lb): about 0.7 ft³ — for laying block and brick, not structural pours
Always check the printed yield on the bag you actually buy; brands round differently.
Estimating notes
- 27 cubic feet make a cubic yard, so 45 bags of 80 lb mix make one yard.
- Over-watering increases apparent volume but cuts compressive strength — mix to the ratio on the bag.
- Yields printed by manufacturers already allow for normal consolidation.