Calculators · Concrete Calculator

Concrete & masonry

Concrete Calculator

Pick what you are pouring, type your measurements and get cubic yards plus the number of 40, 60 and 80 lb bags.

Length

Width

Thickness

Number of identical pieces

Optional. For example, 4 footings of the same size. Empty counts as 1.

Waste to add (%)

Optional. Empty counts as 0%.

How to calculate concrete in cubic yards

Concrete is sold by volume, and in the United States the unit is the cubic yard. One cubic yard is 3 ft × 3 ft × 3 ft, which is 27 cubic feet. Work out the volume in cubic feet with the formula for the shape, then divide by 27.

Shape	Formula, in feet	Example
Slab or footing	length × width × thickness	12 × 10 × 0.5 = 60 ft³ = 2.22 yd³
Wall	length × height × thickness	20 × 4 × 0.6667 = 53.33 ft³ = 1.98 yd³
Round column	π × (diameter ÷ 2)² × height	π × 0.5² × 8 = 6.28 ft³ = 0.23 yd³
Steps	width × run × rise × (1 + 2 + … + steps)	4 × 0.9167 × 0.5833 × 10 = 21.39 ft³ = 0.79 yd³

Thickness is usually measured in inches, so divide it by 12 first. A 4 inch slab is 4 ÷ 12 = 0.3333 ft thick. In the calculator you can leave the thickness in inches and pick the unit from the menu, or type a measurement like 10'6" or 10 ft 6 in in any box.

Example: a 10 ft by 10 ft slab, 4 inches thick

A small patio is 10 ft by 10 ft and 4 inches thick. You decide to add 10% waste. These are the same figures you get if you type them into the “Slab or footing” tab.

Step	Operation	Result
Thickness in feet	4 ÷ 12	0.3333 ft
Volume	10 × 10 × 0.3333	33.33 ft³
Cubic yards	33.33 ÷ 27	1.2346 yd³
With 10% waste	33.33 × 1.10	36.67 ft³ = 1.3580 yd³
80 lb bags	36.67 ÷ 0.60 = 61.11, rounded up	62 bags
60 lb bags	36.67 ÷ 0.45 = 81.48, rounded up	82 bags
40 lb bags	36.67 ÷ 0.30 = 122.22, rounded up	123 bags

How many bags of concrete are in a cubic yard?

A bag makes a fixed amount of concrete, called its yield. Divide the 27 cubic feet of a yard by the yield of your bag. The yields below come from the manufacturer’s data sheet for QUIKRETE Concrete Mix (revised October 2022, checked October 2026). The data sheet says each yield is approximate.

Bag size	Yield per bag	Bags per cubic yard
40 lb	0.30 ft³	90
60 lb	0.45 ft³	60
80 lb	0.60 ft³	45

Sakrete also says that 45 bags of 80 pound mix make a cubic yard. Other brands and special mixes can yield differently, so if your bag prints its own yield, use that figure to check the bag counts. This calculator uses the QUIKRETE yields above.

Common slab sizes at 4 inches thick

Slab size	Cubic feet	Cubic yards	80 lb bags
10 ft × 10 ft	33.33	1.23	56
12 ft × 12 ft	48.00	1.78	80
16 ft × 16 ft	85.33	3.16	143
20 ft × 20 ft	133.33	4.94	223
24 ft × 24 ft	192.00	7.11	320

How much area does a cubic yard cover?

If you already know the square footage, use the “From an area” tab. As a quick check, divide 27 cubic feet by the thickness in feet:

Thickness	One cubic yard covers
3 in	108 sq ft
4 in	81 sq ft
5 in	64.8 sq ft
6 in	54 sq ft
8 in	40.5 sq ft

Measuring walls, columns, post holes and steps

Walls and curbs. A straight curb is a short wall, so use the “Wall” tab with its length, height and thickness.
Columns and post holes. Use the “Round column” tab. Type the diameter of the hole or form and its depth or height. For several identical holes, fill in “Number of identical pieces”.
Steps. The calculator treats every step as a solid block poured from the ground up, so the first step is one rise high, the second is two rises high, and so on. Steps built over fill, or with a hollow core, need less concrete. A landing is a separate slab, so add it on the first tab.
Several areas. Calculate each part on its own and add the cubic yards, or use the quantity box for identical parts.

Bags or a ready-mix truck?

If you mix bags yourself, QUIKRETE’s data sheet advises allowing at least 1 cubic foot of mixer capacity for each 80 lb bag. Its Concrete Mix is designed for pours that are 2 inches thick or more. Ready-mix suppliers sell concrete by the cubic yard and deliver it by truck, so the big figure above is the number to give them.

Add a margin. Cemex suggests adding 10 to 15% to a ready-mix order for spillage, uneven subgrades and other variables. Sakrete suggests adding 10% to every estimate. Type your percentage in the waste box.
Ask about minimums. Cemex states a minimum order of 1 cubic yard per delivery. Other suppliers set their own, so ask before you plan a small pour.
Prices. This calculator does not show prices, because they change by region and supplier. Ask for a quote with your cubic yards in hand.

For a slab, the data sheet also says to cut control joints 1 inch deep every 6 to 8 feet. Your local building code and a structural professional decide the thickness, the reinforcement and the mix for load-bearing work.

Frequently asked questions

How do I calculate how much concrete I need?

Multiply length, width and thickness, all in feet, to get cubic feet. Divide by 27 to get cubic yards. A 10 ft by 10 ft slab that is 4 inches thick is 10 × 10 × (4 ÷ 12) = 33.33 cubic feet, which is 1.23 cubic yards.

How many bags of concrete do I need for a 10x10 slab?

At 4 inches thick the slab needs 33.33 cubic feet. Using the QUIKRETE bag yields, that is 56 bags of 80 lb, 75 bags of 60 lb or 112 bags of 40 lb, rounded up. At 6 inches thick the slab needs 84, 112 or 167 bags.

How many 80 lb bags of concrete make 1 cubic yard?

45 bags, because a cubic yard is 27 cubic feet and QUIKRETE gives about 0.60 cubic feet for an 80 lb bag (27 ÷ 0.60 = 45). A 60 lb bag yields about 0.45 cubic feet, so it takes 60 bags. A 40 lb bag yields about 0.30, so it takes 90. Other brands can differ, so check the yield on your bag.

How many square feet does a cubic yard of concrete cover?

At 4 inches thick, one cubic yard covers 81 square feet, because 27 ÷ (4 ÷ 12) = 81. At 6 inches it covers 54 square feet, and at 3 inches it covers 108.

How much extra concrete should I order?

It depends on the job and the supplier. Cemex suggests adding 10 to 15% to a ready-mix order to cover spillage, uneven subgrades and other variables, and Sakrete suggests adding 10% to every estimate. Type the percentage in the waste box and the calculator adds it for you.

How many cubic feet are in a bag of concrete?

For QUIKRETE Concrete Mix, about 0.30 cubic feet in a 40 lb bag, 0.45 in a 60 lb bag and 0.60 in an 80 lb bag. These yields are approximate and other brands and products can differ, so use the figure printed on your bag.

Is it cheaper to buy bags of concrete or order a truck?

It depends on local prices, which change by region and supplier, so this calculator does not show them. Get the number of bags from the calculator and compare it with a delivery quote. Cemex, for example, states a minimum order of 1 cubic yard per delivery, and other suppliers set their own minimums, so ask yours.