Show the math
- Convert to feet (inches ÷ 12, centimeters ÷ 30.48): Length 16 ft; Width 16 ft; Thickness 4 in = 0.3333 ft
- Volume = 16 × 16 × 0.3333 × 1 = 85.3333 ft³
- Net volume = 85.3333 ft³ ÷ 27 = 3.1605 yd³ (× 0.0283168 = 2.4164 m³)
- Order quantity = 3.1605 yd³ × (1 + 10%) = 3.4765 yd³ = 93.8667 ft³
- 80 lb bags = 93.8667 ft³ ÷ 0.6 ft³ per bag = 156.44 → 157 bags (always round up)
- Weight = 93.8667 ft³ × 150 lb/ft³ = 14,080 lb
What this slab is used for
A 16×16 ft slab (256 ft²) is a big square patio, an outdoor kitchen and dining area, a small workshop floor or the base for a large gazebo or hot-tub enclosure. The square shape gives you a lot of flexibility: a 12 ft circle for a fire pit area fits inside, with room around it for chairs.
Four inches works for a patio. For a workshop with a table saw, a car lift or anything with concentrated weight, 5 or 6 in and a steel grid is the safer plan. Add control joints into a 2×2 grid of 8×8 ft panels, since 16 ft is above the usual spacing for a 4 in slab.
Concrete for a 16×16 ft slab at each thickness
The numbers come to 3.16 yd³ net and 3.48 yd³ with waste at 4 in. That is beyond practical bag mixing (157 bags) and well within a single truck. Many plants charge less per yard for a 3 yd³ order than for a one-yard order, so the cost per square foot falls as the slab gets bigger.
| Thickness | Net yd³ | Order yd³ | Order m³ | 80 lb bags | 60 lb bags | Weight |
|---|---|---|---|---|---|---|
| 3 in | 2.37 | 2.61 | 1.99 | 118 | 157 | 10,560 lb |
| 4 in | 3.16 | 3.48 | 2.66 | 157 | 209 | 14,080 lb |
| 5 in | 3.95 | 4.35 | 3.32 | 196 | 261 | 17,600 lb |
| 6 in | 4.74 | 5.21 | 3.99 | 235 | 313 | 21,120 lb |
The formula is 16 × 16 × thickness ÷ 12 ÷ 27 for the net volume. The order adds 10% for waste and rounds the bag counts up. Use the calculator above for another thickness or waste allowance.
Bags or ready-mix for 16×16 ft?
Bags: 157 bags of 80 lb mix at 4 in, a total of 12,560 lb of dry product. Ready-mix: 3.48 yd³, material about $485–$1,078 at the published range, last verified 2026-10-04, before delivery and short-load fees. Bagged concrete for this slab costs about $864–$1,256. Because the order is above two cubic yards, a truck is usually the practical choice. See bagged vs ready-mix.
What to watch for
- Not enough help. A 16 ft span is too wide to screed from one side by hand without a long board and two people.
- Placing the concrete from only one side, so the far side is placed late and stiff.
- Skipping the joints. At 16 ft the slab will crack somewhere if it has no joints.
- Leaving the gravel base uneven, so the slab ends up thicker in places and uses more concrete.
Layout and joints
Because the footprint is square, a single joint in each direction at the center creates four panels of 8×8 ft, which suits a 4 in slab.
For a 4 in slab, joint spacing of 8 to 12 ft is the usual range, with a 15 ft maximum for any thickness. Read the control joints guide for depth and timing.
Before you order
- Measure the forms, not the excavation, and check the thickness in several places.
- Add the volume of any thickened edge, apron or step separately.
- Plan the base: use the gravel base calculator to estimate stone for 256 ft².
- If the design calls for steel, estimate it with the rebar calculator.
- Put the quantity on the Pour List to combine it with footings and steps.
Frequently asked questions
How many yards of concrete for a 16×16 slab?
3.16 yd³ net at 4 in, 3.48 yd³ with 10% waste.
How many bags of concrete for a 16×16 slab?
157 bags of 80 lb mix or 209 bags of 60 lb mix at 4 in with 10% waste.
How much does a 16×16 slab weigh?
About 14,080 lb (7.04 US tons) at 4 in with 10% waste, using 150 lb/ft³.
How many yards for a 16×16 slab at 6 in?
5.21 yd³ with 10% waste.
How much does a 16×16 concrete slab cost in materials?
About $485–$1,078 for ready-mix concrete at 4 in, before delivery fees, based on the ranges on the cost page (verified 2026-10-04).
Sources
Estimate only. Results depend on the numbers you enter, ground conditions and your supplier. For structural work consult a licensed engineer and follow local codes. Brand names such as Quikrete and Sakrete are used only to cite published product data. This site is not affiliated with any brand.