Concrete Bag Calculator
Quikrete math is simple but unforgiving: run out mid-pour and the cold joint weakens the slab. Enter your slab or post-hole dimensions — you get the volume in cubic feet and yards, plus bag counts for 40, 60 and 80 lb mixes with your chosen waste factor.
How bag counts are computed
Yield per bag: 80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.30 ft³ of mixed concrete. These are the manufacturers' published figures.
The waste factor (10% default) covers spillage, uneven subgrade and mixer residue. Small projects should round up to full extra bags — you cannot buy 0.3 of a bag.
Rule of thumb: one 80-lb bag per fence post is the minimum; two is standard for solid footing. For slabs over about 20 ft³ (a cubic yard is 27 ft³), ready-mix delivery beats bags on both cost and labor.
Frequently asked questions
How many 80 lb bags make a cubic yard?
About 45 bags (27 ft³ ÷ 0.60). At that volume, ready-mix truck delivery is almost always cheaper and far less work.
How much concrete per fence post?
One to two 80-lb bags per post depending on soil and fence height — two is the safe standard for 6-ft privacy fence.
40, 60 or 80 lb bags — which should I buy?
Same concrete, different weight. 80-lb bags are cheapest per cubic foot if you can handle the weight; 40-lb bags suit post holes and small patches.
Related tools
- Bag yields: Quikrete published yield data (80 lb ≈ 0.6 ft³, 60 lb ≈ 0.45 ft³, 40 lb ≈ 0.3 ft³).
Last updated: 2026-09-08