Concrete Patio Calculator

How to measure

Measure the patio between the form boards, not the outside of the stakes. If it is attached to the house, measure out from the foundation or the slab edge. For an L-shaped or curved patio, break it into rectangles and add them with the Pour List.

Plan the size around how the patio will be used. A bistro set needs roughly 10 × 10 ft once chairs are pulled back. A table for six wants 12 × 12 ft or more, and an outdoor kitchen or fire feature can push it past 16 × 20 ft.

Worked example: a 12 × 12 ft patio at 4 in

1. Convert to feet (inches ÷ 12, centimeters ÷ 30.48): Length 12 ft; Width 12 ft; Thickness 4 in = 0.3333 ft
2. Volume = 12 × 12 × 0.3333 × 1 = 48 ft³
3. Net volume = 48 ft³ ÷ 27 = 1.7778 yd³ (× 0.0283168 = 1.3592 m³)
4. Order quantity = 1.7778 yd³ × (1 + 10%) = 1.9556 yd³ = 52.8 ft³
5. 80 lb bags = 52.8 ft³ ÷ 0.6 ft³ per bag = 88 → 88 bags (always round up)
6. Weight = 52.8 ft³ × 150 lb/ft³ = 7,920 lb

You need 1.96 yd³, which is 88 bags of 80 lb mix or 118 bags of 60 lb. A 12 × 12 patio is the largest area most people attempt with bags; bigger patios are better done with a truck so the whole slab is poured in one go.

Patio sizes at a glance

For these exact sizes see the pages for 12 × 12, 12 × 16 and 20 × 20 slabs.

Slope, drainage and thickness

A patio next to a house should slope away from the foundation. A common recommendation is about ¼ in per foot, but check what your local code or builder specifies. On a 12 ft patio that is 3 in of fall, which you build into the base and the forms, not into the concrete thickness. The slope does not change the quantity in a meaningful way, but the extra thickness at the low edge is another reason for the waste allowance.

Four inches is the standard thickness for patios, with 5 or 6 in for areas where a vehicle or heavy hot tub will sit. See the slab thickness guide.

What else goes into a patio

• A compacted gravel base, commonly 4 in. Use the gravel base calculator.
• Reinforcement such as wire mesh or rebar. See the rebar calculator.
• Control joints at roughly 8 to 12 ft for a 4 in slab, or a separate pour per section.
• A finish: broom, stamped or exposed aggregate. Decorative finishes need extra time and often a pro.
• Sealer after curing, particularly in freeze-thaw climates.

Patio mistakes

• Pouring a patio without a slope and living with puddles.
• Tying the patio to the house rigidly. Use an isolation joint at the wall.
• Not allowing for a thicker edge or footing where the patio is raised.
• Underestimating the labor of finishing. Concrete sets on its own schedule, so have enough people.
• Skipping the control joints and getting random cracks.

Compare bags and truck

The concrete cost calculator compares the two routes with your prices. As a rule of thumb, use bags below one yard, compare between one and two, and call a truck above that. Combine the patio with steps or a walkway in the Pour List.

Frequently asked questions