Show the math
- Convert to feet (inches ÷ 12, centimeters ÷ 30.48): Length 12 ft; Width 16 ft; Thickness 4 in = 0.3333 ft
- Volume = 12 × 16 × 0.3333 × 1 = 64 ft³
- Net volume = 64 ft³ ÷ 27 = 2.3704 yd³ (× 0.0283168 = 1.8123 m³)
- Order quantity = 2.3704 yd³ × (1 + 10%) = 2.6074 yd³ = 70.4 ft³
- 80 lb bags = 70.4 ft³ ÷ 0.6 ft³ per bag = 117.33 → 118 bags (always round up)
- Weight = 70.4 ft³ × 150 lb/ft³ = 10,560 lb
What this slab is used for
A 12×16 ft slab (192 ft²) is a common size for a large patio and for the floor of a 12×16 shed or small cabin. It is also long enough for a car, but narrow for a modern parking pad, where 12 ft width is workable but 16 ft in length is short for a full-size sedan or SUV. Treat it as a patio or shed slab first.
Four inches suits a patio. For a workshop shed that will hold a tool bench, a lawn tractor or a workbench with heavy tools, 5 in gives more margin. Put a gravel base under the slab, with the compacted depth as for any slab, and consider light reinforcement.
Concrete for a 12×16 ft slab at each thickness
This is the slab used in the examples on the site: 2.37 yd³ net at 4 in, 2.61 yd³ with 10% waste, which is 118 bags of 80 lb mix. It is a truck job for most people. Ordering 2.61 yd³ will probably be priced as a short load, so ask whether rounding up to 3 yd³ costs much more.
| Thickness | Net yd³ | Order yd³ | Order m³ | 80 lb bags | 60 lb bags | Weight |
|---|---|---|---|---|---|---|
| 3 in | 1.78 | 1.96 | 1.50 | 88 | 118 | 7,920 lb |
| 4 in | 2.37 | 2.61 | 1.99 | 118 | 157 | 10,560 lb |
| 5 in | 2.96 | 3.26 | 2.49 | 147 | 196 | 13,200 lb |
| 6 in | 3.56 | 3.91 | 2.99 | 176 | 235 | 15,840 lb |
The formula is 12 × 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 12×16 ft?
Bags: 118 bags of 80 lb mix at 4 in, a total of 9,440 lb of dry product. Ready-mix: 2.61 yd³, material about $376–$908 at the published range, last verified 2026-10-04, before delivery and short-load fees. Bagged concrete for this slab costs about $649–$944. Because the order is above two cubic yards, a truck is usually the practical choice. See bagged vs ready-mix.
What to watch for
- Long, narrow slabs crack across the short dimension. Cut joints every 8 to 12 ft across the 16 ft side.
- Setting the forms to the wrong thickness, which changes the quantity by hundreds of pounds.
- Running out. A 12×16 slab is large enough that a 1/2 in thickness error over the whole slab is about 0.3 yd³.
- Pouring against a house wall without an isolation joint.
Layout and joints
The 12×16 footprint divides neatly into two 8×12 ft or six 4×8 ft panels, so decide where the joints will go before the forms are set.
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 192 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 12×16 slab?
2.37 yd³ net at 4 in, 2.61 yd³ with 10% waste.
How many bags of concrete for a 12×16 slab?
118 bags of 80 lb mix or 157 bags of 60 lb mix at 4 in with 10% waste.
How much does a 12×16 slab weigh?
About 10,560 lb (5.28 US tons) at 4 in with 10% waste, using 150 lb/ft³.
How many yards for a 12×16 slab at 6 in?
3.91 yd³ with 10% waste.
How much does a 12×16 concrete slab cost in materials?
About $376–$908 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.