Concrete Bag Calculator
Counting bags for a small pour — not paying a truck minimum?
How this is calculated
- Volume in cubic feet = length × width × (depth ÷ 12)
- Order volume = volume × (1 + waste % ÷ 100)
- Bags = ⌈order volume ÷ bag yield⌉ — 80 lb yields 0.60 cu ft, 60 lb yields 0.45, 40 lb yields 0.30 of mixed concrete
Common questions
How many 80 lb bags of concrete for a 4×4 slab?
A 4 × 4 pad at 4 inches is 5.33 cu ft; with 10% waste, call it 10-11 eighty-pound bags. That is a one-person, one-mixer, half-day job — and right at the comfortable limit of hand-mixing before a ready-mix short load becomes the smarter call.
How much does one 80 lb bag of concrete make?
0.60 cubic feet of mixed concrete — a little under two gallons short of a 5-gallon bucket... in practice, one 80 lb bag fills a 12 × 12 × 6 in form with a bit left. Rule of thumb: 45 bags per cubic yard, which is why the math tips toward delivery fast.
When should I stop using bags and order ready-mix?
Around 1 cubic yard (45+ eighty-pound bags), the numbers flip: bagged concrete works out to $180-270/yd³ versus $125-200 for delivered ready-mix — plus about 20 hours of shoveling you do not do. Under a yard, bags still win because trucks have minimum charges.
Can I mix bagged concrete by hand?
Yes, but keep batches small: one 80 lb bag per wheelbarrow mix, water measured to the bag's spec (start with ~3 quarts), and mix it to oatmeal-not-soup consistency. Concrete starts setting 30-60 minutes after water hits it, so stage forms, tools, and a helper before you open the first bag.
What about fast-setting concrete?
Fast-setting (like the red-bag products) is for post setting and repairs, not slabs — it grabs in 15-30 minutes, which is great for a fence post and terrible when you are trying to screed a pad. Regular 80 lb bags reach walking strength in a day or two and full cure in about a week; keep it damp the first few days for maximum strength.