How much concrete is a 40×80 slab?
A 40-by-80-foot slab covers 3200 square feet. At the standard 4-inch thickness that's about 39.51 cubic yards of concrete before waste, or roughly 43.46 yards once you add a 10% allowance. The calculator above is pre-filled to these dimensions — change the thickness or price to match your job.
Concrete for a 40×80 slab by thickness
| Thickness | Concrete to order | 80 lb bags | Material cost |
|---|---|---|---|
| 4″ (standard) | 43.46 yd³ | 1,956 | $6,953 |
| 5″ | 54.32 yd³ | 2,445 | $8,691 |
| 6″ | 65.19 yd³ | 2,934 | $10,430 |
Material cost at $160/yd³ ready-mix, before delivery fees. Cost data updated June 2026.
Common questions
How many yards of concrete for a 40x80 slab?
A 40x80 slab at 4 inches thick needs about 39.51 cubic yards before waste. Add 5-10% extra so you don't come up short. Change the thickness in the calculator above to see how it affects the total.
How many bags of concrete for a 40x80 slab?
At 4 inches thick that's roughly 1956 eighty-pound bags with a 10% allowance. Past about 1 cubic yard (around 45 bags), ready-mix delivery is usually cheaper and far less work than mixing bags by hand.
What does a 40x80 slab cost?
Material alone is a small share of the total. Installed, slabs this size run a wide range depending on thickness, finish, site prep, and region. Use the calculator's installed-cost range as a ballpark, then compare local quotes for a real price.