Concrete Calculator — yards & bags
Figure out exactly how much concrete a slab, footing or post-hole pour needs — in cubic feet, cubic yards, and 40/60/80 lb bags — before you hit the store.
Concrete volume & bag calculator
| Option | Bags needed | Yield |
|---|---|---|
| 80 lb bags | 667 | 0.60 cu ft each |
| 60 lb bags | 889 | 0.45 cu ft each |
| 40 lb bags | 1334 | 0.30 cu ft each |
Volume = length × width × depth (in feet). Standard bag yields (printed on the bag): 80 lb ≈ 0.6 cu ft, 60 lb ≈ 0.45 cu ft, 40 lb ≈ 0.3 cu ft. Always buy ~5–10% extra and verify yields on the bag you purchase.
Job-site tips
- Order 5–10% extra — forms swell, the ground is never perfectly flat, and running out mid-pour is expensive.
- Ready-mix minimums: most plants have a ~1–2 cu yd minimum, so for small slabs bags are cheaper than a truck.
- Post holes: for a 4×4 or 6×6 post, use the pier diameter and depth of the hole, not the post — the concrete fills the hole.
- Mixing time: use a mixer or drill paddle for slabs; hand-mixing more than ~10 bags in a wheelbarrow is very slow.
FAQ
How much concrete do I need for a 10×10 slab 4 inches thick?
Convert 4 in to 0.333 ft, then 10 × 10 × 0.333 = 33.3 cu ft = 1.23 cu yd. At 0.6 cu ft per 80 lb bag, that is 56 bags (add ~10% waste: 62 bags). Ordering ready-mix, 1.5 cu yd is the practical minimum for most plants.
What is the yield of an 80 lb bag of concrete?
An 80 lb bag of standard concrete mix yields about 0.6 cubic feet (0.022 cu yd). 60 lb bags yield about 0.45 cu ft and 40 lb bags about 0.3 cu ft. Exact yields are printed on the bag and vary slightly by mix.
How many bags of 80 lb concrete are in a cubic yard?
A cubic yard is 27 cu ft. At 0.6 cu ft per 80 lb bag, you need 45 bags per cubic yard (27 ÷ 0.6 = 45). With 60 lb bags (0.45 cu ft) it is 60 bags, and with 40 lb bags (0.3 cu ft) it is 90 bags.