Concrete Calculator

Multiply length × width × thickness in feet and divide by 27 for cubic yards. A 10 × 10 ft patio 4 inches thick takes 1.23 cubic yards, which is 56 bags of 80 lb concrete mix.

Updated October 19, 2026 · How we calculate

1. Measure the area

Length

Width

Units

For an L-shape or an odd yard, split it into rectangles, circles and triangles. We add them up.

2. How thick?

Thickness

Units

Common thicknesses

Source: Quikrete, Concrete Sidewalks and Small Slabs; Quikrete, Concrete Patios; Quikrete, Concrete Driveways and Curbs

3. Which concrete?

Concrete

Standard concrete mix for slabs, walks, patios and pads. Weighs about 3,780 to 4,050 lb per cubic yard.

Source: Iowa DOT Materials IM 340; American Concrete Institute, Concrete Terminology; Quikrete Concrete Mix 1101 data sheet (2022)

4. Extras(optional)

Add extra for waste and settling

The ready-mix industry advises ordering 4 to 10% over the measured volume. If the ground is 1/8 inch low, a 4-inch slab takes about 3% more concrete.

Source: NRMCA, Concrete in Practice 8: Discrepancies in Yield

Your local price

Prices vary a lot by area. Check with your supplier or the store shelf, then type it here.

Worked example

A 10 × 10 ft patio, 4 inches thick:

Area: 10 × 10 = 100 square feet
Depth in feet: 4 ÷ 12 = 0.3333 ft
Volume: 100 × 0.3333 = 33.33 cubic feet
Cubic yards: 33.33 ÷ 27 = 1.235 cu yd
Weight: 1.235 × 3,780 to 4,050 lb ÷ 2,000 = 2.33 to 2.5 tons
Bags: 33.33 ÷ 0.6 = 56 80 lb bags
Bags: 33.33 ÷ 0.45 = 75 60 lb bags
Bags: 33.33 ÷ 0.375 = 89 50 lb bags
Bags: 33.33 ÷ 0.3 = 112 40 lb bags

Source: Iowa DOT Materials IM 340; American Concrete Institute, Concrete Terminology; Quikrete Concrete Mix 1101 data sheet (2022)

How to choose and how deep

How thick

Sidewalks: at least 4 inches.
Patios: 4 inches.
Driveways: 4 inches for cars, 5 or 6 inches for trucks and heavy vehicles.

Source: Quikrete, Concrete Sidewalks and Small Slabs; Quikrete, Concrete Patios; Quikrete, Concrete Driveways and Curbs

Order a little extra

Ground is never perfectly flat. The ready-mix industry advises 4 to 10% over the measured volume, and the calculator adds it if you choose.

Source: NRMCA, Concrete in Practice 8: Discrepancies in Yield

How bag counts work

Each bag size yields a set volume once mixed. Divide your cubic feet by that yield and round up. Bags are sold by weight, but the yield is what matters.

Source: Quikrete Concrete Mix 1101 data sheet (2022); Sakrete High-Strength Concrete Mix technical data sheet

Quick reference

Bag	Yield	Bags per cubic yard	Bags for 10 sq ft at 4 in
80 lb	0.6 cu ft	45	6
60 lb	0.45 cu ft	60	8
50 lb	0.375 cu ft	72	9
40 lb	0.3 cu ft	90	12

Source: Quikrete Concrete Mix 1101 data sheet (2022); Sakrete High-Strength Concrete Mix technical data sheet

Questions people ask

How many 80 lb bags of concrete make a yard?

45. An 80 lb bag yields about 0.60 cubic feet, and a cubic yard is 27 cubic feet.

Source: Quikrete Concrete Mix 1101 data sheet (2022)

How many bags of concrete do I need for a 10 × 10 slab?

At 4 inches thick, 56 bags of 80 lb or 75 bags of 60 lb, before any extra for waste.

Source: Quikrete Concrete Mix 1101 data sheet (2022)

How thick should a concrete patio be?

4 inches is the usual thickness for a patio or sidewalk. Driveways for cars need 4 inches; for trucks, 5 or 6.

Source: Quikrete, Concrete Patios; Quikrete, Concrete Driveways and Curbs

How much extra concrete should I order?

4 to 10% over the measured volume, to cover uneven ground and spills.

Source: NRMCA, Concrete in Practice 8: Discrepancies in Yield

How much does a yard of concrete weigh?

About 3,780 to 4,050 pounds: normal concrete weighs 140 to 150 pounds per cubic foot.

Source: Iowa DOT Materials IM 340; American Concrete Institute, Concrete Terminology