Concrete Patio Cost Calculator

Which way does the water go?

This is the question to ask first, before thickness, before finish, before anything. A patio is a few hundred square feet of waterproof surface being added directly against the house, and every drop that lands on it has to go somewhere that is not the foundation.

The number is a quarter of an inch of fall per foot, sloping away from the house. On a 14 foot deep patio that is three and a half inches of drop from the wall to the outer edge — enough that you can see it if you look along the surface, and far more than most people expect.

Get it wrong and the failure is not cosmetic. Water pooling against a foundation finds its way into a basement, saturates the soil that holds the footing, and in a freezing climate lifts the whole slab. A patio that drains back toward the house is the single most expensive mistake available on this job, and it costs nothing to avoid on the day.

Two things to confirm before the pour:

• The slope, stated as a number. "It'll drain fine" is not an answer. A quarter inch per foot, away from the building.
• Where the water goes once it leaves the slab. Onto lawn that can take it, or into a drain. Not onto a neighbor's lot, and not into a flower bed six inches below the slab edge that will wash out by the second summer.

The joint where it meets the house

A patio should not be bonded to the foundation. It should be separated from it by an isolation joint — a compressible strip, usually half-inch foam or fiber, running the full length of where the slab meets the wall.

The reason is that the slab and the house move independently. The patio is on the top few feet of soil, which freezes, swells, dries and shifts with the seasons; the foundation is on a footing below all of that and barely moves at all. Pour them tight together and the slab either cracks along the wall or starts lifting the siding and trim above it.

The second reason is water. A hairline gap between slab and foundation is a channel straight down the outside of the wall. A proper isolation joint, caulked at the top with a flexible sealant and re-caulked every few years, closes it.

This is a five-dollar detail that gets left out constantly, and the only time to put it in is before the concrete arrives.

Size it for the furniture, not for the yard

The most common way a patio costs more than it needed to is being bigger than anything that will ever stand on it. Useful dimensions:

• A table and four chairs, with room to pull a chair back: about 10 by 10 feet, 100 sq ft.
• A table and six chairs: about 12 by 14, 170 sq ft.
• The same plus a grill station and two loungers: about 300 sq ft, which is why that is the default on the calculator above.
• A dining area and a separate seating area: 400 to 500 sq ft.

A patio needs about 3 feet of clearance behind a pulled-out chair and a minimum depth of 12 feet to hold a dining set without anybody sitting on the edge. Below about 10 feet deep it stops being a room and becomes a path, however long it is.

Measure the furniture you own or intend to buy, add the clearances, and pour that. Six hundred square feet of concrete nobody stands on is $2,000 of nothing.

What you are paying for

For a 300 sq ft patio on bare ground with a broom finish, at $3,225:

Labor is the biggest line and the concrete itself is under a fifth of the total, which is why small patios cost so much more per square foot than large ones. The crew still has to show up, set up, form, and come back to cut joints whether the slab is 150 square feet or 600. At 150 sq ft this works out to about $13.80 per square foot; at 1,000 it is about $8.60.

If you are getting a patio and a walkway, or a patio and a driveway, pouring them on the same day is worth real money. One mobilization, one concrete delivery, one set of forms being moved rather than built twice.

Four inches, and the one case that needs five

Four inches on a compacted base with welded wire mesh is the standard patio and is right for furniture, a grill and people.

The case for five inches with a rebar grid is a hot tub. Filled and occupied, a six-person tub is two to three tons sitting on a footprint of about 40 square feet — a point load several times anything else a patio carries. The other case is expansive clay soil that lifts in winter, where the steel is doing the work rather than the inch.

Six inches is for a slab something will be driven onto, or a slab that will have a roof structure on posts bearing into it.

Thickness and steel move together in the trade: four inches gets mesh, five or six gets rebar, and nobody pours six inches with nothing in it. An extra inch is a quarter more concrete across the whole slab, which is why the step up shows in the price.

Stamped concrete, honestly

Stamping adds about 75% to the cost of a patio, and it is worth knowing what that buys and what it commits you to.

What it buys: the look of stone or brick for considerably less than stone or brick, in one continuous surface with no joints for weeds to grow in.

What it commits you to:

• Resealing every 2 to 3 years. The color sits in the top layer and the sealer is what protects it. Let the sealer go and the color goes with it, unevenly.
• It is slippery when wet unless a grit additive goes into the sealer. Beside a pool, insist on it.
• Repairs show. A cracked or spalled section cannot be patched to match a stamped pattern, which is the opposite of pavers, where a damaged unit lifts out and a new one drops in.
• The result depends entirely on the crew. The mats go on in a short window while the slab is still plastic, and there is no second attempt. Ask to see three finished jobs at least two years old, not photos from the week of the pour.

Exposed aggregate adds about 18% instead, washes the cement off the top to leave the stone showing, hides staining far better than a smooth finish, and needs no maintenance beyond what plain concrete needs. It is the quieter upgrade and the one more people should look at.

Before you can use it

• Walk on it: 24 to 48 hours.
• Put furniture on it: 7 days.
• Fill a hot tub on it: 28 days, with no exceptions worth taking.
• Seal it: 28 days for most sealers, and check the product.

Keep it damp for the first few days in hot, dry weather, or confirm a curing compound went on. Concrete does not dry out, it reacts with water, and a surface that loses its water too fast ends up crazed and dusty.

Concrete, pavers, or a deck

• Concrete is the cheapest per square foot of the three, lasts 25 to 40 years, needs almost nothing done to it, and cannot be patched invisibly.
• Pavers run roughly 40 to 80% more, last longest, and have the one advantage that matters over a long horizon: a settled, stained or cracked section lifts out and is relaid. Their weakness is joint sand and weeds.
• A deck costs more than concrete per square foot and needs ongoing work, but it is the only option that makes sense where the ground falls away. Anything more than about 18 inches above grade is a deck, because the fill and retaining needed to bring a slab up to level costs more than the framing.

On flat ground close to the house, concrete wins on price and effort. On a slope, it stops being a fair comparison.

Questions worth asking

• What is the slope, in inches per foot, and which way?
• Is there an isolation joint at the house wall?
• What base is going in, how deep, and is it being compacted or raked?
• How far apart are the control joints, and when are they being cut? Within 24 hours, in panels as near square as the shape allows.
• What psi mix? 4,000 psi with air entrainment where it freezes; 3,000 is thin for an exterior slab.
• Where does the excavated soil go — in the price, or your problem?
• If it is stamped: three jobs at least two years old, and is grit going into the sealer?
• Who is responsible if water ends up against the foundation? Ask it out loud. The answer tells you how carefully the slope will be set.