How Much Concrete for a 16x40 Slab?
A 16 by 40 foot slab is 640 square feet. How much concrete for a 16x40 slab at the common 4-inch thickness: about 7.90 cubic yards. Most people order 8.75 yards to cover waste and an uneven base.
Concrete calculator →The math for a 16x40 slab
- Area: 16 ft × 40 ft = 640 sq ft.
- Thickness in feet: 4 in ÷ 12 = 0.333 ft.
- Volume: 640 × 0.333 = 213.3 cubic feet.
- Cubic yards: 213.3 ÷ 27 = 7.90 yd³.
- With 10% extra: 8.69 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Concrete for a 16x40 Driveway?
Concrete for a 16x40 slab by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 213.3 | 7.90 | 8.69 | 356 | 475 |
| 5 in | 266.7 | 9.88 | 10.86 | 445 | 593 |
| 6 in | 320.0 | 11.85 | 13.04 | 534 | 712 |
Bag counts assume about 0.60 cubic feet per 80 lb bag and 0.45 per 60 lb bag, rounded up.
Thickness for this job
Four inches is the usual thickness for patios, walks and shed floors. Slabs that carry cars or a heavy hot tub are often poured at 5 to 6 inches, and edges are sometimes thickened where loads concentrate.
Related: How Much Gravel for a 16x40 Driveway?
Placing the order
Ready-mix is priced and batched by the cubic yard (27 cubic feet). Plants commonly add a small-load fee when an order is under a set minimum, so ask about it when you call. Ordering a little extra costs far less than a second truck.
Prep before the pour
Under the slab, most residential pours sit on about 4 inches of compacted gravel. The base spreads the load, drains water away and keeps the slab from cracking as the soil freezes and thaws. Compact the base in thin lifts, and dampen it just before the pour so it does not pull water out of the mix.
Joints and reinforcement
Plan the joints before the pour. Panels close to square crack less than long, narrow ones, and joint spacing around 10 feet is typical for a 4-inch slab. Cut joints with a groover while the concrete is soft or with a saw within the first day.
Questions people ask
How many yards of concrete for a 16x40 slab at 4 inches?
About 7.90 cubic yards, or 8.69 with 10 percent extra.
How many yards for a 16x40 slab at 6 inches?
About 11.85 cubic yards.
How many 80 lb bags for a 16x40 slab?
About 356 bags at 4 inches thick, before any waste allowance.
How many square feet is a 16x40 slab?
640 square feet.
Should I add extra for waste?
Yes. Adding 5 to 10 percent covers uneven base, spillage and form bulges.
When is bagged concrete practical?
Usually for jobs under about a cubic yard. Beyond that, mixing dozens of bags by hand gets slow and batches may not blend well.
Related guides
- How Much Area Does a Yard of Concrete Cover?
- How Many Bags of Concrete in a Yard? 40, 60, 80 lb
- Gravel Base Under a Concrete Slab: Depth and Tons
- How Many Yards in a Concrete Truck? Mixer Sizes
- Concrete Short Load Fee: What It Is and How to Cut It
- 60 lb vs 80 lb Concrete Bags: Yield, Count, and Cost
- Rebar vs Wire Mesh in a Slab: Which One to Use
- Cost to Pour a Concrete Slab: Per Square Foot
- How Much Concrete for a 16x35 Slab?
- How Much Concrete for a 16x36 Slab?
As an Amazon Associate, AsphaltTons.com earns from qualifying purchases. Product links below are sponsored.