How to Plan and Pour a Concrete Patio Slab
A concrete patio is a durable, low-maintenance project you can plan in an afternoon. This guide walks through sizing, thickness, base prep, and exactly how much concrete to order.
Ready to run the numbers? Use our Concrete Calculator or the Concrete Slab Calculator to get an instant material estimate.
1. Choose the size and thickness
Start from how you will use the patio. A 10×10 ft slab seats a small table and four chairs; 12×16 ft comfortably fits a dining set and walk-around room. Mark the outline with stakes and string, then measure the final length and width in feet.
Thickness drives the concrete volume more than anything else. A patio that carries only foot traffic is poured 4 in thick. Go to 5–6 in if the slab will support a grill island, hot tub, or vehicle traffic.
- 4 in — standard patios, walkways, and shed pads (foot traffic only).
- 5 in — patios with heavy furniture, grills, or fire pits.
- 6 in — slabs that will see vehicle loads or a hot tub.
2. Prep the base and set forms
Excavate to the slab thickness plus 4–6 in of compacted gravel base. A level gravel base drains water away from the concrete and prevents settling cracks. Use 2×4 or 2×6 lumber for forms, staked every 3–4 ft, and check that the top of the form is level.
- 4–6 in of compacted gravel (3/4 in crushed stone with fines packs best).
- Forms staked level and braced against the wet concrete pressure.
- Rebar (#4 on 24-in centers) or wire mesh for slabs 5 in and thicker.
- Expansion board against any existing slab or foundation wall.
3. Calculate how much concrete you need
Concrete is ordered in cubic yards. The volume is length × width × thickness, converted to yards. Always add a waste allowance for spillage, uneven subgrade, and over-excavation.
Source: 1 cubic yard = 27 cubic feet. Thickness in inches is divided by 12 to get feet.
A 12×12 ft patio at 4 in thick: 12 × 12 × (4÷12) = 48 ft³ ÷ 27 = 1.78 yd³. With 10% waste: 1.96 yd³ to order, or about 88 eighty-pound bags if you mix by hand.
Under about 1 cubic yard, bagged mix is practical. Above 1 yard, delivered ready-mix is usually cheaper and far less labor. Use the calculators below to get an exact number for your dimensions.
4. Pour, screed, and finish
Pour all at once if possible, working from one end to the other. Screed with a straight 2×4 riding on the forms, then float the surface to close it up. Add control joints every 8–10 ft (or 2–3× the slab thickness in feet) to control where it cracks. Cure slowly by misting and covering with plastic for at least 7 days.
Frequently asked questions
How thick should a concrete patio be?
4 in for foot traffic only. Go 5–6 in if the patio will carry a grill island, hot tub, or any vehicle load. Thicker slabs resist cracking under point loads.
How much concrete do I need for a 12×12 patio?
A 12×12 ft slab at 4 in thick needs 1.78 yd³ before waste, or about 1.96 yd³ with a 10% allowance. That is roughly 88 eighty-pound bags if you mix by hand.
Do I need rebar in a patio slab?
For a 4 in patio, wire mesh is usually enough. For 5–6 in slabs or anything carrying weight, use #4 rebar on 24-in centers. Control joints every 8–10 ft matter more than reinforcement for preventing random cracks.
Calculators for this guide
Put these numbers to work with the free calculators referenced above.