How much concrete do I need for a patio slab?
Concrete volume for a poured patio slab of a given size and thickness
A 12 ft x 12 ft patio at 4 inches thick takes about 1.8 cubic yards of concrete, or roughly 2 cubic yards once you add a 10% waste factor.
The numbers below assume the inputs in the assumptions section. Change any of them in the calculator to fit your own project.
Pouring a patio is one of the most common DIY concrete jobs, and the question that decides your order is volume. Volume depends on three things: the patio footprint, the slab thickness, and a small allowance for waste. Patio area on its own is not enough, because a 4-inch slab and a 6-inch slab over the same footprint differ by half again as much concrete.
This page works through a standard 12-foot by 12-foot patio at 4 inches thick, then hands you the calculator so you can swap in your own length, width, and thickness. Ready-mix is sold by the cubic yard, so the goal is to land on a yardage you can order with confidence rather than guessing and coming up short mid-pour.
Prefer the full version with the explanation and examples? Open the calculator page directly.
Open the concrete volume calculator144 square feet of slab surface.
Standard for a foot-traffic patio; step up to 5-6 in if a hot tub or vehicle will sit on it.
Covers spillage, an uneven subgrade, and slight over-excavation.
A wavy base quietly raises how much concrete the slab swallows.
Ready-mix is sold by the yard, so the final figure is rounded to a yardage you can order.
A 12 ft x 12 ft patio poured 4 inches thick
- 1Convert the thickness to feet: 4 in / 12 = 0.33 ft.
- 2Find the slab volume: 12 ft x 12 ft x 0.33 ft = 48 cubic feet.
- 3Convert to cubic yards, the way ready-mix is sold: 48 / 27 = 1.78 cubic yards.
- 4Add the 10% waste factor: 1.78 x 1.10 = 1.96 cubic yards.
Order 2 cubic yards for a 12 ft x 12 ft patio at 4 inches thick. If you bump the thickness to 6 inches, the same footprint needs closer to 3 cubic yards, so confirm the thickness before you place the order.
- Sizing the order from patio area alone. A 144 sq ft patio is not 144 of anything until you multiply by thickness.
- Pouring too thin. Four inches is the practical minimum for a patio; thinner slabs crack under foot traffic and freeze-thaw cycles.
- Dropping the waste factor. Spillage and a slightly low subgrade can eat 5-10% of the load, and running short means a cold joint.
- Mixing units. Keep length, width, and thickness in the same system, and convert inches to feet before multiplying.
- Ignoring the gravel base. The base sets the slab depth; if it dips, the slab thickens and your yardage climbs.
How much concrete do I need for a 12x12 patio?
A 12 ft by 12 ft patio at 4 inches thick needs about 1.78 cubic yards of concrete, or roughly 2 cubic yards once you add a 10% waste factor. Pour it 6 inches thick and the same footprint climbs to about 3 cubic yards.
How thick should a patio slab be?
Four inches is the standard thickness for a patio that carries foot traffic and patio furniture. Step up to 5 or 6 inches if a hot tub, outdoor kitchen, or vehicle will rest on it, since the extra load needs a thicker, reinforced slab.
Why add a waste factor to a concrete order?
Some concrete is lost to spillage, and an uneven subgrade often takes more than the nominal thickness. A 10% allowance keeps you from running short during the pour, which would otherwise force a cold joint where fresh concrete meets a set edge.
How many bags of concrete equal one cubic yard?
A cubic yard is a lot of bagged concrete. An 80-pound bag yields about 0.6 cubic feet, so a cubic yard (27 cubic feet) is roughly 45 bags. For anything beyond a couple of cubic yards, ready-mix delivery is usually cheaper and far less work.
Do I need a gravel base under a patio slab?
Yes. A compacted gravel base, usually 4 inches, drains water, resists frost heave, and gives the slab a level bed. The base also fixes the slab depth, so compacting it well keeps your concrete order from creeping up.