Concrete Patio Materials List: What to Buy for a 12×12 Slab
A 12 × 12 ft patio poured 4 inches thick needs 1.96 cubic yards of concrete (with 10% extra), about 3.0 tons of gravel for the base, 12 twenty-foot lengths of #3 rebar, and 6 eight-foot boards for the forms. This is the full shopping list, with how each number was worked out, and a chart for other sizes.
The materials list
| What to buy | How much | How we worked it out |
|---|---|---|
| Concrete | 1.96 yd³ (ready-mix), or 88 bags of 80 lb | Concrete calculator: 4 in thick, 10% extra. Above about 1 yd³, ready-mix is usually the better buy |
| Compacted gravel base | 3.0 tons (2.1 yd³) of crushed stone | Gravel calculator: 4 in deep, plus 20% because loose stone compacts |
| Rebar, #3 (3/8 in) | 12 bars of 20 ft | Rebar calculator: a grid at 16 in centers, 10% extra for laps. Or about 3 sheets of 5 × 10 ft wire mesh |
| Rebar chairs | About 9 | About one for every 4 × 4 ft, so the steel sits mid-slab and not on the gravel |
| Form boards | 6 boards of 8 ft (2×6) | The 48 ft perimeter, divided by 8 ft boards. A 2×6 on edge makes a form for a 4 in slab |
| Stakes for the forms | About 20 | One every 2 to 3 feet along the forms, plus at the corners |
| Expansion joint strip | 12 ft | Along the edge where the patio meets the house or any other slab |
| Curing and finishing | 1 kit | Broom, edger, groover, float, and plastic sheeting or a curing compound |
Your numbers will differ if your patio is not a plain rectangle or if you want a different thickness. Change them in the concrete calculator, or use the chart below.
Materials for other patio sizes
4 inch slab, 4 inch gravel base, #3 rebar at 16 in centers, with the waste allowances above:
| Patio size | Concrete | 80 lb bags | Gravel | Rebar (20 ft bars) | Form boards (8 ft) |
|---|---|---|---|---|---|
| 10 × 10 ft | 1.36 yd³ | 62 | 2.1 tons | 9 | 5 |
| 12 × 12 ft | 1.96 yd³ | 88 | 3.0 tons | 12 | 6 |
| 12 × 16 ft | 2.61 yd³ | 118 | 4.0 tons | 16 | 7 |
| 16 × 20 ft | 4.35 yd³ | 196 | 6.6 tons | 26 | 9 |
Before you order
- Call 811 (in the US) a few days before you dig, so buried lines are marked, and ask your building department whether a patio needs a permit or has a setback from the property line.
- Decide how you will pour. A 12 × 12 slab is more than a yard and a half of concrete, which is about 88 bags of 80 lb: too much to mix by hand before the first batch sets. Ordering ready-mix and having two or three helpers is the usual choice. See the bags of concrete guide.
- Plan the slope. Set the forms so the patio falls about 1/4 inch per foot away from the house.
- Check the weather. Avoid pouring in heavy rain or when the temperature is near freezing.
How the job goes
- Mark out the patio, then dig about 8 inches below the finished surface: 4 inches for the base and 4 for the slab. Compact the soil.
- Spread the gravel in layers and compact each one, until the base is a firm, level 4 inches.
- Set the forms on stakes at the right height and slope, and check them with a level and string.
- Lay the rebar on chairs, tie the crossings, and keep it a few inches in from the edges.
- Pour, then screed (strike off) the surface level with a straight board, and float it.
- Edge the slab, cut or tool control joints, and finish the surface with a broom for grip.
- Cure it: keep the slab damp, or covered, for about a week so that it gains strength slowly. Remove the forms after a day or two.
Mistakes that cost people money
- Skipping the compacted base. A slab poured on soft soil will settle and crack.
- Adding extra water to make the concrete easier to work. It makes the finished slab weaker.
- No control joints. Concrete cracks as it shrinks, and joints decide where.
- Finishing while bleed water is still on the surface. Wait for the sheen to go, then float and finish.
- Ordering too little. A short pour leaves a cold joint, so always order 5 to 10% extra.
Other projects: a paver patio is more forgiving of ground movement and can be built in stages. Estimates only: check your local code, and follow the product labels.
Frequently asked questions
How much concrete do I need for a 12x12 patio?
A 12 × 12 ft patio 4 inches thick needs 1.78 cubic yards before waste, and 1.96 cubic yards with 10% extra. Ready-mix is ordered in set amounts, so round up to the next quarter yard.
How many bags of concrete for a 12x12 patio?
80 bags of 80 lb mix for a 4 inch slab with no waste, or 88 with 10% extra. That is too much to mix by hand before it starts to set, so most people order ready-mix.
How thick should a concrete patio be?
Four inches is the usual thickness for a patio that carries people and furniture. A slab that will carry a vehicle or heavy equipment is usually 5 to 6 inches, and your local code and soil can change that.
Does a concrete patio need a gravel base?
Yes. A 4 inch compacted gravel base gives the slab even support and lets water drain away. For this size it is about 3.0 tons of crushed stone, including 20% for compaction.
Does a patio slab need rebar?
Reinforcement does not stop concrete cracking, but it holds the cracks tight. Many patios use rebar or wire mesh: a #3 grid at 16 inch centers takes 12 bars of 20 ft for this size.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.