Concrete Patio Calculator

How it's calculated

The calculator finds the volume in cubic feet: length (ft) × width (ft) × thickness (in ÷ 12). That's converted to cubic yards by dividing by 27. A waste percentage is added on top to cover over-excavation, form loss, and cutting around curves or a joint layout, and the adjusted cubic yardage is multiplied by concrete's density to get the weight in tons. Bag counts divide the adjusted cubic feet by each bag's yield; ready-mix truckloads divide the adjusted cubic yards by the truck's capacity.

Worked example

A 10 ft × 12 ft patio poured 4 inches thick: volume = 10 × 12 × (4 ÷ 12) = 40 cubic feet. In cubic yards, that's 40 ÷ 27 = 1.48 yd³. Adding a 10% waste factor: 1.48 × 1.10 = 1.63 yd³. At 2.02 tons per cubic yard, that's 1.63 × 2.02 = 3.29 tons — or 3.18–3.31 tons across the 1.95–2.03 density range. In 80 lb bags, the adjusted 44 cu ft (40 × 1.10) would need 74 bags — past the point where ready-mix usually makes more sense, though still within reach of a determined DIY pour.

How deep should it be?

A patio behaves differently from a driveway or footing in one big way: it has to shed water, not just bear weight. The slab needs to slope away from the house so rain and runoff drain toward the yard rather than pooling against the foundation — getting this wrong is one of the more common causes of basement or crawlspace moisture problems traced back to a DIY patio. The exact slope and drainage path depend on your yard's grading, where the water needs to go, and sometimes a local drainage or stormwater ordinance, so this is worth planning with whoever pours the slab rather than guessing at a ratio. Surface finish is a separate decision from thickness or slope: a broom finish adds slip resistance and is the common default for an exterior surface that gets wet, while a smoother trowel finish, a stamped pattern, or an exposed-aggregate finish are all achievable with the same base slab and just change the final pass during the pour. Control joints — the tooled or saw-cut lines that let the slab crack in a straight, planned line instead of a random one as it shrinks while curing — need a layout plan too; spacing depends on the slab's thickness and panel shape, and getting it wrong shows up later as an uncontrolled crack instead of a clean joint line. None of these are numbers this calculator supplies — it converts the area and thickness you already have into a volume and weight; the slope, finish, and joint layout are decisions to make with whoever's pouring the patio, or from ACI's own guidance on slab-on-grade construction.

Common mistakes

• –Pouring a patio flat or sloped toward the house instead of away from it — even a small mistake here can send water toward the foundation instead of away from it.
• –Not planning a surface finish before the pour. Finish is applied during placement (broom, trowel, stamp, exposed aggregate) — deciding after the concrete is down isn't an option for most finishes.
• –Skipping a control joint layout, or spacing joints without a plan. Concrete shrinks as it cures and will crack somewhere — a joint layout decides where; skipping it leaves that to chance.
• –Assuming a patio's thickness is always thinner than a driveway's. It depends on what the patio needs to support — check your specific load and soil conditions rather than assuming.
• –Forgetting that a wetter, richer finishing mix (common for a smooth trowel or stamped finish) can behave differently during cure than a standard structural mix — ask your ready-mix supplier about finish-specific mix considerations before ordering.

Where the density figure comes from

Unlike the landscape materials on this site, concrete is a manufactured product with a tightly controlled mix, so its density varies far less than gravel, sand, or mulch — and the same figure applies whether it's poured as a slab, a patio, or any other normal-weight element. CEMEX, a major ready-mix producer, puts a solid unbroken pour at about two tons (4,000 lbs) per cubic yard. ACI 318 and ASTM C138 define normal-weight concrete at 145–150 lb/ft³ — ACI 318 uses 150 lb/ft³ as its default structural value — which works out to 3,915–4,050 lbs (1.96–2.03 tons) per cubic yard. The 1.95–2.03 ton/yd³ range here reflects that normal-weight span, not moisture variation. Lightweight and heavyweight concrete mixes fall outside this range and aren't covered by this calculator. We use 2.02 tons/yd³ as the display figure, drawn from:

• CEMEX — Ready-Mix Concrete Calculator
• ACI 318 & ASTM C138 — normal-weight concrete density, 145–150 lb/ft³

Read more in our density methodology.

FAQ

How much concrete do I need for a patio?

A 12 ft × 14 ft patio at 4 inches thick needs about 2.07 cubic yards before waste — use the calculator above to add your waste factor and get a bag count or ready-mix order.

Which way should a patio slope?

Away from the house, so rain and runoff drain toward the yard instead of pooling against the foundation. The exact slope and drainage path depend on your yard's grading and where the water needs to go — plan this with whoever pours the slab rather than guessing at a ratio.

What concrete finish should I use for a patio?

It depends on the look and slip resistance you want. A broom finish is the common default for an exterior surface that gets wet, since it adds texture underfoot. A trowel finish, a stamped pattern, or an exposed-aggregate finish are all possible with the same base slab — finish is applied during placement, so decide before the pour.

How far apart should control joints be on a patio?

It depends on the slab's thickness and panel shape, not a fixed number. Joints are tooled or saw-cut lines that let the slab crack in a planned, straight line as it shrinks while curing — skipping the layout leaves that crack to chance instead. Plan the layout with whoever pours the slab, or check ACI's guidance on slab-on-grade construction.

Is a patio thinner than a driveway?

Usually, since a patio only carries foot traffic while a driveway carries vehicle loads — but it's not automatic. What a specific patio needs depends on its load and the soil underneath, so check your situation rather than assuming a patio is always thinner.

Should I use bags or ready-mix for a patio?

It depends on size. A small patio can stay within reach of a bagged DIY pour, but past roughly half a cubic yard, ready-mix delivery is generally cheaper and far less labor than mixing dozens of bags by hand.

Why does concrete's weight vary so little compared to gravel or sand?

Concrete is a manufactured product with a tightly controlled mix ratio, so its density is far more consistent than a quarried or organic material's. The range on this site comes from ACI 318 and ASTM C138's normal-weight concrete specification (145–150 lb/ft³), the same figures used across every concrete calculator here, not from moisture swings the way gravel, sand, or mulch vary.