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Concrete Volume Calculator

Length × width × thickness, converted to the cubic yards your ready-mix supplier will quote.

Length (ft)

Width (ft)

Thickness (in)

Concrete needed

1.235 yd³

Order 5-10% extra to account for spillage and uneven subgrade.

What you entered

Length (ft): 10Width (ft): 10Thickness (in): 4

1
Slab volume in cubic feet
10 × 10 × (4/12)= 33.3333 ft³
2
Convert to cubic yards
33.3333 ÷ 27= 1.2346 yd³

Result

Concrete needed: 1.235 yd³

A 10 × 10 ft slab at 4 inches thick needs about 1.2345679012345678 cubic yards of concrete.

Cubic yards of concrete for common slab sizes at 4, 5, and 6 inch thickness

Each figure is length times width times thickness divided by 27, the same arithmetic the calculator runs, with no overage added. Values are rounded to two decimals; the calculator shows more places.

Slab size (ft)	Slab area (sq ft)	4 in thick (cu yd)	5 in thick (cu yd)	6 in thick (cu yd)
8 x 10 shed pad	80	0.99	1.23	1.48
10 x 10 patio	100	1.23	1.54	1.85
10 x 12 patio	120	1.48	1.85	2.22
12 x 12 patio	144	1.78	2.22	2.67
12 x 16 patio	192	2.37	2.96	3.56
16 x 20 slab	320	3.95	4.94	5.93
20 x 20 slab	400	4.94	6.17	7.41
12 x 40 driveway	480	5.93	7.41	8.89
24 x 24 garage	576	7.11	8.89	10.67

These are exact volumes with no waste allowance. Order 5 to 10 percent more than the figure shown, because subgrade is never perfectly level and a short pour creates a cold joint that permanently weakens the slab. Ready-mix is delivered in cubic yard increments and most suppliers set a minimum order plus a short-load fee, so anything under about half a yard is usually cheaper to mix from bags at roughly 45 bags of 80 lb premix per cubic yard. Thickness follows use: 4 inches for patios and walkways, 4 to 6 for driveways and garage floors, and whatever your local code specifies for footings.

Always order a little extra

Uneven subgrade, spillage, and minor measurement error mean ordering exactly the calculated amount often comes up short — 5-10% extra is standard practice, and running out mid-pour is far worse than a little leftover.

Ready-mix is sold by the cubic yard

Concrete trucks deliver in cubic yard increments, and most suppliers have a minimum order — check with your supplier before finalizing a small pour, since it may be cheaper to bag your own concrete for very small jobs.

Frequently asked questions

My patio is 12 ft x 10 ft x 4 inches thick — how much concrete do I need?

About 1.48 cubic yards (12 x 10 x 0.333 ft = 40 cubic feet / 27 = 1.48 cu yd). Order 1.6 cu yd to include the standard 5-10% overage for uneven subgrade and spillage.

How many bags of concrete is 1 cubic yard?

About 45 bags of 80-lb premix or 60 bags of 60-lb premix per cubic yard. For anything over about 0.5 cubic yards, ready-mix delivery is usually cheaper and significantly less labor than mixing bags by hand.

Should I order extra concrete?

Always order 5-10% more than calculated. Running short mid-pour creates a cold joint (weak seam). Leftover concrete is a minor waste; a short pour can compromise the entire slab.

What thickness should my concrete slab be?

Standard residential patios and walkways: 4 inches. Driveways: 4-6 inches (6 for heavy vehicles). Garage floors: 4-6 inches. Footings: per your local building code, typically 8-12 inches.