Before starting any concrete construction work, it is important to calculate the exact volume of the material needed. An insufficient amount of concrete would force you to make two pours in two successive passes, resulting in a structurally weak joint between the two poses; moreover, it would also result in a waste of money. Fortunately, to determine the square footage of concrete areas it is sufficient to calculate the volume of the space to be filled and add 5-10%, to be on the safe side. For laying concrete for foundations, which requires the filling of three-dimensional areas, the volume is calculated using the equation length x width x height.
Steps
Method 1 of 2: Using Cubic Equations
Step 1. Try to become familiar with measuring the volume of concrete
The volume of concrete (the amount of physical space it occupies) is usually measured in cubic meters. A cubic meter is a cube whose sides measure one meter.
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Usually on the packaging of dry concrete bags the volume of the “wet” cement obtained by mixing it with the right amount of water is specified. Below you will find rough estimates of how many bags of dry concrete are needed for one cubic meter of wet concrete.
- 40 kg bag: 56 bags per 1 cubic meter.
- 32 kg bag: 71 bags per 1 cubic meter.
- 26 kg bag: 86 bags per 1 cubic meter.
Figure Concrete Yardage Step 2 Step 2. Divide your project into rectangular prisms
Compared to other three-dimensional shapes, the volume of a rectangular prism is relatively easy to calculate, therefore, if possible, it is preferable to divide your entire design into one or more rectangular prisms. For example, if your project includes a single rectangular plate, that will be your only prism. However, if you have to fill a slab and four straight walls, each wall will represent a prism, resulting in five prisms.
A rectangular prism is a three-dimensional shape with six sides, all rectangular; the opposite facades in a rectangular prism are parallel to each other. Put simply, a rectangular prism can be thought of as any box with straight edges
Figure Concrete Yardage Step 3 Step 3. Calculate the volume of each prism
The volume of a rectangular prism can be calculated by multiplying length by width by height. For example, in the next steps we will imagine filling a slab measuring 3.05m long, 3.66m wide and 10.16cm deep.
Figure Concrete Yardage Step 4 Step 4. Transform all values into the same unit of measurement
The length and width of the slab are given in meters, but its height is given in centimeters. In our equation the same unit of measurement must be used for each parameter.
To transform centimeters into meters divide the value reported in centimeters x 100. A slab measuring 10, 16 cm deep will be deep 0, 10 m. To transform the measurement back into centimeters, multiply x 100.
Figure Concrete Yardage Step 5 Step 5. Find the volume of the prism using the formula:
Volume = Length * Width * Height. Multiply the three measurements together to calculate the volume of the prism.
In our example the volume of the slab is 3.05 m x 3.06 m x 0.10 m = 1, 12 cubic meters.
Figure Concrete Yardage Step 6 Step 6. Convert the volume to cubic meters if necessary
The slab volume is 39.6 cubic feet, but unfortunately concrete is usually measured in cubic yards. One cubic yard equals 27 cubic feet, so to convert to cubic yards we can divide the value of cubic feet x 27. The slab volume is 39.6 / 27 = 1.47 cubic yards. Alternatively, since there are three feet in a yard, we can divide each measurement in feet by three and get the equivalent measurements in yards and then multiply these together and we will have the same result.
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Often concrete is also measured in cubic meters. In our example we have already calculated this value. However, if you need to convert cubic yards to cubic meters, know that:
- 1 cubic yard = 0.764554858 cubic meters
- 1 cubic meter = 1.30795062 cubic yards
Figure Concrete Yardage Step 7 Step 7. Find the volume of the other prisms as described above
If your project includes more than one prism, calculate the volume of each of them separately, using the previous method. At the end add all the volumes to know the total volume. Pay attention that the prisms are not overlapping, to avoid counting the concrete twice and buying more product than necessary.
Figure Concrete Yardage Step 8 Step 8. Calculate the volume of any irregular shapes
Not all projects can easily be divided into rectangular prisms. If you have a non-homogeneous area, for example, you cannot accurately approximate its shape using rectangular prisms. To calculate the volume of an irregular shape, first find the cross-sectional area of the shape. Then multiply the area by the length of the shape. For example, if the base area of a column is 2.74 m in length and that of the cross section is 0.21 square meters, then the volume will be 2.74 x 0.21 = 0.58 meters cubes.
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Also you could use some simple equations to calculate the volume of some non-rectangular shapes. Here are some of the most common:
- Cylinder: Volume = (π) r2 × h, where “r” is the radius of the circle at both ends of the cylinder and “h” is its height.
- Triangular prism: Volume = 1/2 bh1 × l, where "b" is the length of the base of one of the triangular facades, "h1"is its height, and" l "is its length.
- Sphere: Volume = (4/3) (π) r3, where "r" is the radius of the circle representing the circumference of the sphere. While you are unlikely to have to fill a perfect sphere, remember that many dome shapes are nothing more than "half spheres".
Figure Concrete Yardage Step 9 Step 9. Purchase some more concrete than necessary
It is a good general rule to add 5-10% to the calculated volume, in consideration of the high incidence of the scrap or in the case of deeper excavations. Since you can't expect to use concrete with 100% yield, get more than you need. For example, if you predicted a total volume of 15.3 cubic meters, then you should get 1.05 x 15.3 = 16.1 cubic meters.
If you use steel fiber reinforced concrete, these will replace some of the volume of the concrete, but you usually don't have to consider them in your calculations, they will remain unaffected
Figure Concrete Yardage Step 10 Step 10. Convert volume to weight if needed
Pre-dosed concrete is sold by volume, but bags of concrete mix are retailed by weight. Often on the packages of the mixture there are indications on the weight or the volume obtained from each bag. Concrete weighs around 2400 kg per cubic meter. Therefore, if you need 1.53 cubic meters of concrete, then you need 3672 kg (1.53 x 2400) of concrete. As mentioned above, it is preferable to purchase more than necessary - the remainder can be used later.
Method 2 of 2: Quick Calculation Applicable to Foundation Plates
Figure Concrete Yardage Step 11 Step 1. Make sure the space for pouring concrete is a rectangular prism
Construction companies have come up with a quick and easy way to calculate the square footage of concrete needed for a given pour. This method does not involve the use of any equation, however it requires two conditions. First, it only applies to rectangular prisms (box-shaped castings); this method is simpler for relatively shallow castings, but can be applied to all rectangular prisms. Second, it requires that the measurements of the length and width of the area to be filled are expressed in meters and the depth in centimeters. Remember that:
- 1 yard = 3 feet
- 12 inches = 1 foot
- 1 meter = 3.28 feet
- 30, 48cm = 1 foot
Figure Concrete Yardage Step 12 Step 2. Calculate the area of the zone to be filled
Area is a two-dimensional measure typically used for flat surfaces. To calculate the area of your concrete project, multiply the length by the width of the area, leaving out its depth.
- For example, suppose you need to fill a rectangular prism that is 7 meters wide, 1.50 meters long and 15 cm deep (0.15 meters). Its area will be 7 x 1, 50 = 10, 5 square meters. For the moment we ignore its depth.
- Remember that this method only works for rectangular prisms. In other words, the area to be filled must have straight vertical edges.
Figure Concrete Yardage Step 13 Step 3. Divide the area by a numerical coefficient
After finding the area, you need to divide its value by a certain number - the thicker your concrete slab, the smaller the number; the thinner the plate, the higher the number. Below you will find the coefficients for the most common thicknesses. If your thickness isn't listed below, don't worry - you'll learn how to easily calculate the coefficient in the next step.
- If your project is about 10cm thick, divide the area by 81;
- If your project is about 15cm thick, divide the area by 54;
- If your project is about 20cm thick, divide the area by 40;
- If your project is about 30cm thick, divide the area by 27.
Figure Concrete Yardage Step 14 Step 4. Manually calculate the other coefficients
If the thickness of the area to be filled does not fit in any of the previous examples, you can quickly calculate the coefficient by dividing 324 by the thickness of your concrete project (in centimeters). Next, divide the area by the result to determine the meters.
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For example, suppose the area of 10.5 square meters has a depth of about 15 cm. We will find the cubic meters of concrete needed as follows:
- 324/15 = 21, 6
- 10, 5/21, 6 = 0, 48 cubic meters
