How Much Concrete for a 16×16 Slab?
Quick Answer
A 16×16 foot slab poured 4 inches thick needs 3.16 cubic yards of concrete. Order about 3.5 cubic yards to cover a 10% waste factor. At 256 square feet, ready-mix delivery is far more practical than mixing bags.
- 4-inch slab: 3.16 cubic yards (85 cubic feet)
- Order ~3.5 cubic yards with 10% waste
- Bag equivalent: ~142 80-lb bags or ~190 60-lb bags
- Ready-mix cost: $474–$553 delivered
Formula
Multiply length, width, and thickness (in feet) to get cubic feet, then divide by 27 to convert to cubic yards. For a 4-inch slab, thickness is 4 ÷ 12 = 0.333 ft.
Step-by-Step Calculation
- 1
Slab volume in cubic feet
16 × 16 × 0.333 = 85.3 cubic feet
- 2
Convert to cubic yards
85.3 ÷ 27 = 3.16 cubic yards
- 3
Add 10% waste
3.16 × 1.10 = 3.5 cubic yards
- 4
Bag equivalent (80-lb)
85.3 ÷ 0.6 cu ft per bag = 142 bags
16×16 Slab Concrete by Thickness
| Thickness | Cubic Feet | Cubic Yards | 80-lb Bags | Ready-Mix Cost* |
|---|---|---|---|---|
| 4 inches | 85 | 3.16 | 142 | $474–$553 |
| 5 inches | 107 | 3.95 | 178 | $593–$691 |
| 6 inches | 128 | 4.74 | 213 | $711–$830 |
*Ready-mix at $150–$175 per cubic yard delivered. A 256 sq ft pour is well past the point where bags make sense.
Pro Tips
- At 3.16 cubic yards (3.5 with waste), you clear the typical 3-yard short-load threshold at most ready-mix plants, meaning standard pricing with no surcharge. This is the sweet spot for residential concrete work — enough volume for efficient truck delivery but small enough for a 3-person crew.
- For a 16×16 slab, cut one control joint across the center in each direction (forming 4 equal 8×8 sections). Use a groover tool while the concrete is plastic to cut to 1/4 of the slab depth. These pre-scored lines control where inevitable shrinkage cracks appear.
- Set up one form board as a screed rail running through the center of the slab so you can screed 8-foot sections rather than trying to pull a 16-foot screed board. Remove the center rail after screeding and fill/float the resulting groove.
- If this slab will support a hot tub, pergola, or heavy storage, use 5,000 PSI concrete instead of the standard 3,000 PSI. The cost increase is only $5–$10/yard ($15–$35 total) but nearly doubles the compressive strength.
Key Cost Factors
- Ready-mix at 3.5 yards × $120–$160/yd = $420–$560. Sub-base gravel (2 yards): $70–$100. Form lumber and stakes: $50–$80. Wire mesh or rebar: $60–$100. Total DIY materials: $600–$840. This is the most cost-efficient concrete slab size for DIY — large enough to justify ready-mix but small enough for a small crew.
- A contractor quotes $1,500–$2,600 for a 16×16 slab ($6–$10/sq ft). DIY saves $900–$1,760 in labor. At 256 sq ft, the DIY-to-contractor savings ratio is excellent — you save more per hour of your time than on smaller slabs where concrete mixing dominates the labor.
Common Mistakes to Avoid
- Hand-mixing the whole thing. At about 3.16 cubic yards for 4 inches, a 16×16 slab is a ready-mix job; bag-mixing invites cold joints and exhaustion.
- No waste buffer. Order around 3.4 yards to cover spillage and uneven sub-grade rather than the exact calculated volume.
- Weak base over 256 sq ft. Compact 4 inches of gravel evenly; any soft spot becomes a crack in a slab this large.
- Skipping reinforcement. Wire mesh or rebar keeps shrinkage cracks tight across the wide surface.
Related Project Considerations
- Set thickness by use. Keep 4 inches for a patio; go 5–6 inches with rebar for vehicles or heavy structures.
- Grid the control joints. Divide the 16×16 into four 8×8 panels with saw-cut or tooled joints to steer cracking.
- Check truck reach. Ensure the ready-mix chute can reach the forms or plan for a pump or wheelbarrow crew.
Frequently Asked Questions
How many bags of concrete for a 16×16 slab?
A 4-inch thick 16×16 slab needs about 142 bags of 80-lb concrete or 190 bags of 60-lb concrete, including waste. That is far too many to mix by hand — ready-mix delivery is cheaper per cubic yard and saves an entire day of labor. Hand-mixing 140+ bags also risks inconsistent batch strengths and cold joints between pours, both of which weaken the finished slab.
How thick should a 16×16 slab be?
Four inches suits patios, garden sheds, and outdoor seating areas that carry only foot traffic and furniture. Step up to 5 or 6 inches for garages, workshops, or any surface bearing vehicles or heavy equipment. Always pour over a minimum 4 inches of compacted gravel base for drainage and to prevent the slab from settling unevenly as the soil beneath shifts with moisture and temperature changes.
How much does a 16×16 concrete slab cost?
Materials run $474–$830 depending on thickness (4 vs 6 inches). A professionally poured and finished 16×16 slab costs $1,536–$3,072 (about $6–$12 per sq ft) including labor, forming, gravel base, reinforcement, and finishing. Add 10–15% for sites requiring demolition of an existing surface, significant grading, or decorative finishes like broom texture or stamped patterns.