How Much Concrete for a 20x20 Patio?
For a 20x20 patio poured 4 inches thick, plan on about 4.94 cubic yards of concrete. That comes from 400 square feet times 0.333 feet of depth, divided by 27. How much concrete for a 20x20 patio at other thicknesses is in the table below.
Concrete calculator →The math for a 20x20 patio
- Area: 20 ft × 20 ft = 400 sq ft.
- Thickness in feet: 4 in ÷ 12 = 0.333 ft.
- Volume: 400 × 0.333 = 133.3 cubic feet.
- Cubic yards: 133.3 ÷ 27 = 4.94 yd³.
- With 10% extra: 5.43 yd³.
The concrete calculator runs the same steps for any size and thickness.
Related: How Much Gravel for a 20x20 Patio?
Concrete for a 20x20 patio by thickness
| Thickness | Cubic feet | Cubic yards | Yards +10% | 80 lb bags | 60 lb bags |
|---|---|---|---|---|---|
| 4 in | 133.3 | 4.94 | 5.43 | 223 | 297 |
| 5 in | 166.7 | 6.17 | 6.79 | 278 | 371 |
| 6 in | 200.0 | 7.41 | 8.15 | 334 | 445 |
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 Pea Gravel for a 20x20 Patio?
Truck or bags?
A cubic yard of concrete is 27 cubic feet and weighs roughly 4,000 pounds. Most ready-mix trucks carry up to about 9 to 10 yards, though local trucks and rules vary. If your total is under a yard or two, bagged mix or a short-load supplier may be cheaper.
Prep before the pour
Under the slab, most residential pours sit on about 4 inches of compacted gravel. The base spreads the load, drains water away and keeps the patio from cracking as the soil freezes and thaws. Compact the base in thin lifts, and dampen it just before the pour so it does not pull water out of the mix.
Joints, mesh and rebar
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 a 20x20 patio at 4 inches?
About 4.94 cubic yards, or 5.43 with 10 percent extra.
How many yards for a 20x20 patio at 6 inches?
About 7.41 cubic yards.
How many 80 lb bags for a 20x20 patio?
About 223 bags at 4 inches thick, before any waste allowance.
How many square feet is a 20x20 patio?
400 square feet.
How much does a cubic yard of concrete weigh?
Roughly 4,000 pounds, or about 2 tons, for normal-weight concrete.
How thick should the base under the slab be?
About 4 inches of compacted gravel is common for residential slabs, more on soft or poorly drained soil.
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 16x24 Patio?
- How Much Concrete for an 18x18 Patio?
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