How Much Concrete for an 18x18 Patio?
For an 18x18 patio poured 4 inches thick, plan on about 4.00 cubic yards of concrete. That comes from 324 square feet times 0.333 feet of depth, divided by 27. How much concrete for an 18x18 patio at other thicknesses is in the table below.
Concrete calculator →The math for an 18x18 patio
- Area: 18 ft × 18 ft = 324 sq ft.
- Thickness in feet: 4 in ÷ 12 = 0.333 ft.
- Volume: 324 × 0.333 = 108.0 cubic feet.
- Cubic yards: 108.0 ÷ 27 = 4.00 yd³.
- With 10% extra: 4.40 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Concrete for an 18x18 Slab?
Concrete for an 18x18 patio by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 108.0 | 4.00 | 4.40 | 180 | 240 |
| 5 in | 135.0 | 5.00 | 5.50 | 225 | 300 |
| 6 in | 162.0 | 6.00 | 6.60 | 270 | 360 |
Bag counts assume about 0.60 cubic feet per 80 lb bag and 0.45 per 60 lb bag, rounded up.
Choosing the thickness
Four inches is standard for a patio that sees foot traffic and furniture. Slope it about 1/8 to 1/4 inch per foot away from the house so rain runs off, and go thicker under a hot tub or outdoor kitchen.
Related: How Much Paver Base for an 18x18 Patio?
Ordering ready-mix
Concrete is ordered by the cubic yard, and a yard is 27 cubic feet. Ready-mix plants usually sell in quarter- or half-yard steps, so round up to the next step rather than down. Running short in the middle of a pour leaves a cold joint, which is a weak seam in the patio.
Base and forms
Uneven ground is the main reason pours run short. Every half inch of extra depth across the patio adds concrete you did not plan for. Screed the base flat, check it with a string line and set the forms to finished height before the truck arrives.
Joints and reinforcement
Reinforcement does not stop cracks, but it holds them tight. Wire mesh or rebar set mid-depth on chairs is common for a patio that carries vehicles; fiber-reinforced mix is an option for light-duty slabs. Joints about 10 feet apart control where cracks form.
Questions people ask
How many yards of concrete for an 18x18 patio at 4 inches?
About 4.00 cubic yards, or 4.40 with 10 percent extra.
How many yards for an 18x18 patio at 6 inches?
About 6.00 cubic yards.
How many 80 lb bags for an 18x18 patio?
About 180 bags at 4 inches thick, before any waste allowance.
How many square feet is an 18x18 patio?
324 square feet.
How much does a cubic yard of concrete weigh?
Roughly 4,000 pounds, or about 2 tons, for normal-weight concrete.
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 16x20 Patio?
- How Much Concrete for a 16x24 Patio?
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