How to Figure Concrete Yardage
Two Methods:
Before beginning any concrete placement job, it is important to determine the correct volume of concrete needed for the job. An insufficient amount of concrete may cause you to have to make a concrete placement in 2 separate steps, which will create a structurally weak seam between the 2 placements. Too much, on the other hand, may be a waste of money. Fortunately, figuring out a project's concrete yardage is usually a simple matter of calculating the volume of the space to be spilled and then adding 510% to this number to be conservative. For basic concrete placements calling for concrete to be poured into a rectangular 3D area, calculating volume is done with the equationlength × width × height.
Steps
Using 3D Volume Equations

Familiarize yourself with how concrete volume is measured.Concrete's volume (the amount of physical space it takes up) is typically measured in either cubic yards (yds3) or cubic meters (m3). A cubic yard is a 3dimensional cube that is 3 feet long in each dimension, while a cubic meter is a cube that is 1 meter long in each dimension.
 Typically, bags of dry concrete mix will specify the volume of "wet" concrete each bag will make when properly mixed with water. Below are rough estimates for how many bags of dry concrete mix it takes to make one cubic meter of wet concrete:
 40 kg bag: 56 bags to make 1 cubic meter
 32 kg bag: 71 " " " 1 cubic meter
 26 kg bag: 86 " " " 1 cubic meter
 Typically, bags of dry concrete mix will specify the volume of "wet" concrete each bag will make when properly mixed with water. Below are rough estimates for how many bags of dry concrete mix it takes to make one cubic meter of wet concrete:

Break your concrete project up into different rectangular prisms.Compared to other 3D shapes, a rectangular prism's volume is relatively easy to calculate, so, if possible, it is best to break your entire project up into one or more rectangular prisms. For example, if your project calls for you to pour a single rectangular slabongrade, that slab would be your only prism. However, if you need to pour a slab along with 4 straight walls, each wall would be its own prism, resulting in a total of 5 prisms.
 A rectangular prism is a threedimensional shape with six faces, all of which are rectangles; opposite faces in a rectangular prism are parallel to each other.In layman's terms, a rectangular prism can be thought of as any "boxy" shape with straight edges.

Calculate the volume of each prism.A rectangular prism's volume can be found by multiplying itslength times its width times its height.For example, in the next few steps, let's imagine that we're pouring a slab that is 10 feet (3.05 m) long, 12 feet wide (3.66 m), and 4 inches (10.16 cm) deep.

Convert all measurements to the same units.Our slab's length and width are given in feet and meters, but its height is given in inches and centimeters. For our volume equation to work, all measurements must be in the same units, so we must convert. Since there are 12 inches per foot, we should divide our inch value by 12 to get a value for feet. The slab is 4 / 12 =0.33 feetdeep.
 To convert from centimeters to meters, simply divide a centimeter value by 100. A slab that is 10.16 cm deep is 10.16 / 100 =0.10 metersdeep. To convert back to centimeters, multiply by 100.

Find the volume of the prism using the formula:Volume = Length * Width * Height. Multiply the 3 dimensions together to arrive at the prism's volume. In our example, the slab's volume is 10 ft × 12 ft × 0.33 ft =39.6 cubic feet.
 To find the metric equivalent, we use our meter measurements instead of our feet measurements. 3.05 m × 3.66 m × 0.10 m =1.12 cubic meters.

Convert the volume into cubic yards or cubic meters as needed.The slab's volume above is expressed as 39.6 cubic feet, but, unfortunately, concrete is usually measured in cubic yards. There are 27 cubic feet in a cubic yard, so, to convert to cubic yards, we can divide by our cubic feet value by 27. The slab's volume is 39.6 / 27 =1.47 cubic yards. Alternatively, since there are three feet in a yard, you can divide each individual foot measurement by 3 to get yard values and then multiply these together to get the same answer.
 Concrete is also often measured in cubic meters. In our example problem, we already found this value. However, in the case that you need to convert between cubic yards and cubic meters, know that:
 1 cubic yard = 0.764554858 cubic meters
 1 cubic meter = 1.30795062 cubic yards
 Concrete is also often measured in cubic meters. In our example problem, we already found this value. However, in the case that you need to convert between cubic yards and cubic meters, know that:

Find additional prism volumes as above.If you have more than one prism in your concrete pour, calculate each one's volume individually using the above method. Finally, add all of the volumes together to arrive at your total volume for your project. Be careful that none of your prisms overlap, or you will end up counting some of the concrete twice, which can lead to you buying more than you need.

Calculate the volume of any irregularlyshaped forms.Not every concrete job can be easily split up into rectangular prisms. If you have a spread footing in your concrete design, for example, you can't accurately approximate its shape using rectangular prisms. To find the volume of an irregular form, first find the area of a crosssection of the form. Then, multiply that area times the length of the form. For example, if a spread footing is 3 yards (2.74 m) long and has a crosssectional area of 0.25 square yards (0.21 square meters), then the volume is 3 × 0.25 = 0.75 cubic yards (or 2.74 × 0.21 = 0.58 cubic meters).
 Additionally, some common nonrectangular shapes have convenient equations to find their volume. Below are a few of the most common:
 Cylinders: Volume = (Pi)r2× h, where "r" is the radius of the circle at either end of the cylinder and "h" is the height of the cylinder.
 Triangular Prisms : Volume = 1/2bh1× l, where "b" is the length of the base of one of the triangular faces, "h1" is its height, and "l" is the length of the prism.
 Spheres: Volume = (4/3)(Pi)r3, where "r" is the radius of the circle that represents the sphere's circumference. While it's unlikely that you'll ever have to pour a perfect sphere, note that many domelike shapes are just spheres cut in half.
 Additionally, some common nonrectangular shapes have convenient equations to find their volume. Below are a few of the most common:

Buya littlemore concrete than you need.A good rule of thumb is to add 5 to 10 percent to your figured volume to account for spillage, waste, or overexcavation. Because you can't reasonably expect to use your concrete with 100 percent efficiency, be sure to order more than you actually need. For instance, if you have figured a total volume of 20 cubic yards (15.3 cubic meters), then you should order 1.05 × 20 = 21 cubic yards (or 1.05 × 15.3 = 16.1 cubic meters).
 If you are pouring steelreinforced concrete, the steel reinforcing will displace some of your concrete's volume. Usually, you don't need to consider this in your calculations. This will keep your figures on the conservative side.

Convert your volume figure to weight, if necessary.Truckmixed concrete is sold by volume, but bags of concrete mix are sold in retail establishments by weight. Often, dry mix will have information on the bag indicating the "wet" weight or volume each bag produces. Concrete weighs about 4000 pounds per cubic yard (2400 kg per cubic meter). So, if you need 2 cubic yards (1.53 cubic meters) of concrete, then you need (2 * 4000) or 8000 pounds, or (1.53 * 2400) or 3672 kg of concrete. As noted above, buying more dry concrete mix than is needed is usually much safer than buyinglessconcrete mix than is needed  unused mix can always be used in the future.
Quick Method for Basic Slabs

Ensure your concrete pour is a rectangular prism.Contractors have devised a quick, easy system of determining how much concrete yardage is needed for a given pour. This method doesn't require you to use any volume equations  however, there are two stipulations for its use. First, it only works for rectangular prisms (basic "boxshaped" pours). This method iseasiestfor relatively shallow pours, but it's possible for all rectangular prisms. Second, it requires that your pour area's length, and width measurements be in feet and that its depth measurement be in inches. To convert any of your measurements to feet, use the conversion factors below:
 1 yard = 3 feet
 12 inches = 1 foot
 1 meter = 3.28 feet
 30.48 centimeters = 1 foot

Find the square footage of the area you're pouring.Square footage (written "sq. ft" or ft2) is a measure of 2dimensional area typically used to describe floor space. To determine your concrete job's square footage, simply multiply the length and width of the area you're pouring into without taking into account its depth.
 For example, let's say we're pouring into a rectangular prism that is 10 ft wide, 5 feet long, and 6 inches (0.5 feet) deep. Its square footage would be 10 × 5 = 50 sq. feet. We don't need to worry about its depth yet.
 Remember, this method only works for rectangular prisms. In other words, your pour area must have straight vertical edges.

Divide your square footage by a numerical coefficient.Now that you've found your square footage, all you need to do to find your project's concrete yardage is to divide the square footage by a certain number  thethickeryour project, the smaller the number; thethinneryour project, the larger the number. Below are coefficients for a few common thicknesses. If your project's thickness isn't listed below, don't worry  you'll learn how to easily figure out your coefficient in the next step.
 If your project is 4 inches thick, divide your square footage by 81 to determine your yardage.
 If your project is 6 inches thick, " " " " " 54.
 If your project is 8 inches thick, " " " " " 40.
 If your project is 12 inches (1 foot) thick, " " " " " 27.

Determine odd coefficients manually.If the thickness of your concrete pour doesn't match any of the examples above, you can quickly calculate it by dividing 324 by the thickness of your concrete project (in inches). Then, divide your square footage by your answer to find your project's yardage.
 For example, let's say our 50 sq. ft concrete pour is 7 inches deep. We would find our concrete yardage as follows:
 324/7 = 46.28
 50/46.28 =1.08 cubic yards.
 For example, let's say our 50 sq. ft concrete pour is 7 inches deep. We would find our concrete yardage as follows:
Community Q&A

QuestionI have to pour a concrete slab 15' x 11' x 10" thick. What is the correct math?wikiHow ContributorCommunity Answer15 x 11 x (1 / 6 * 5) = 137.5 cubic feet 137.5 x 0.037037 = 5.092593 cubic yardsThanks!

QuestionI am making a horseshoe pit. Both pits are 5'x4'x8" deep. How much sand do I need, and how much will it weight?wikiHow ContributorCommunity AnswerYou will need 1.5 tons of a washed river sand or 1 cubic yard.Thanks!

QuestionWhy do I not get the same yardage using the two methods?wikiHow ContributorCommunity AnswerThere are two different ways to get it, but they will both end up equaling the same thing. Check your math and that you've converted any measurements to the units required.Thanks!

QuestionHow can I calculate cubic yards of an area that is shaped like a 'T'?wikiHow ContributorCommunity AnswerDivide it into two separate rectangles and calculate the horizontal part of the T first, and the vertical part of the T second. Then add the amounts together.Thanks!

I have an uneven slab that is 17 feet wide, 30 ft long, 5 inches on 1 end and 15 on the opposite end. How many yards will the slab be?

How do I tell how much concrete I need?

How do I calculate a round slab of concrete?

What if my slab isn't square?

How can I write a letter describing the dimensions of a concrete floor that is 13 feet wide, 26 feet long and 4 inches thick, made of fiber mixed concrete rated at 3000 PSI?
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