Concrete Calculator: How Much Concrete Do You Need?CASAPLORERTrusted & Transparent
Amount of Concrete Bags Needed
|Number of 40lb Concrete Bag(s)||Number of 60lb Concrete Bag(s)||Number of 80lb Concrete Bag(s)|
How to Calculate Concrete Using This Concrete Calculator
This concrete calculator can be used to estimate the volume of concrete needed for concrete slabs, walls, stairs, footings, columns, curbs, and gutters. You can also enter a custom concrete density and price to find out how much concrete would be needed, the number of bags of concrete required, and the total cost of concrete.
How Do I Find Out How Much Concrete I Need?
Concrete is made up of cement, water, sand, and gravel. The concrete needed would depend not only on the volume of concrete, but on the density of concrete. Stronger concrete would have a higher density, which would require more concrete material for the same volume. You may also need a gravel base layer to pour your concrete slab onto. This allows for drainage and prevents water damage. A gravel calculator can be used to estimate how much gravel you will need.
The most common concrete density is 150 lbs per cubic foot. That means that one cubic foot would require 150 lbs of concrete. High density concrete, which can have a density of 375 lbs per cubic foot or more, will require more concrete. Low density concrete, with a density of 115 lbs per cubic foot or less, will require less concrete. By default, this concrete calculator uses a density of 150 lbs per cubic foot to calculate the amount of concrete needed for your project.
A good rule of thumb is to always have room for error and to purchase more concrete than needed. A typical buffer would be 5% to 10% more concrete than your estimated need.
The intended use of the concrete will also determine the amount of concrete needed. For uses that will require a lot of compressive strength for long periods of time, such as driveways or exterior concrete slabs with heavy loads, a high compressive strength would be required. Driveways and commercial floors generally require a compressive strength of 4,000 pounds per square inch (PSI). This translates to 27.58 megapascal (MPa). Uses that require less strength, such as fence posts, might only require a strength of 2,500 PSI. You can use a fence calculator to estimate the number of fence posts required for a certain distance.
Concrete Volume Formulas
Square or Rectangular Concrete Slab
The formula for calculating the volume of a concrete slab is:
Concrete Slab Volume = Length x Width x Thickness
The length and width of concrete slabs are usually measured in feet, but the thickness of slabs are typically measured using inches. The most common concrete slab thickness is 4 inches for residential uses, but slabs can be as thick as 6 inches or more for driveways and other uses with heavy loads. Home foundations will also require thicker concrete slabs, along with concrete footings. Homes that are constructed on concrete slabs happen to be the cheapest construction type when looking at the costs of building a home. Concrete slabs for finished basements that don’t support the home can have a thickness that is less than home foundations.
Typical Concrete Slab Thickness
|Use||Concrete Slab Thickness|
|Residential Floors||4 inches|
|Roads||6 - 10 inches|
|Highways and Major Roads||12+ inches|
Calculating the volume of concrete walls is similar to calculating the volume of concrete slabs. The difference is that you will use the wall height and length, rather than a slab's width and length.
To calculate the volume of concrete walls:
Concrete Wall Volume = Wall Height x Wall Length x Wall Thickness
Concrete Stairs and Steps
To calculate the volume of stairs, you will need to divide the stairs up into different sections.
The first part to calculate is the platform, which is the walking area at the top of the stairs. The platform volume would be the depth of the platform multiplied by the width of the stairs, then multiplied by the height of the stairs. You can calculate the height of the stairs by measuring the rise of each step, multiplied by the number of steps.
Calculating the volume of the steps themselves can be more complicated. You will need to calculate the volume of each step, and then add them all up. The volume of each step would be the width of the stairs multiplied by the step's run, then multiplied by the height of the step. The step's height would be the rise of each step multiplied by the step’s number.
For example, if a concrete stair had three steps, then to calculate the total volume:
Stair Run x Stair Width x (Stair Rise x 1)
Stair Run x Stair Width x (Stair Rise x 2)
Stair Run x Stair Width x (Stair Rise x 3)
This equals the volume of the steps. You would then add the volume of the platform to get the total volume of the concrete stairs.
Concrete footings are used in foundations. The calculation is similar to a concrete wall, but instead of height, you'll measure the depth of the footing.
Concrete Footing Volume = Length x Width x Depth
The size of concrete footings will depend on how strong the soil is. If the soil is weak, then a larger footing would be needed to support the foundation. For example, if the soil can't support a lot of weight, the footing might need to have a width of 25 inches. If the soil can support a lot of weight, you might be able to use concrete footings with a width of just 10 inches. The depth of footings will also depend on the soil type and climate.
Columns can be round or rectangular. For round columns, you will need to find the radius of the column, which would be the column diameter divided by two. The volume for the column can be calculated using the formula for a cylinder:
Volume of a Concrete Round Column: π x r2 x Column Height
Square and rectangular columns are similar to walls and other rectangular shapes.
Volume of a Concrete Square/Rectangular Column: Length x Width x Height
Concrete Curbs and Gutters
Curbs and gutters are commonly found alongside roadways, but concrete curbs can also be used in residential landscaping and hardscaping. Similar to stairs, the formula for calculating the volume of curbs and gutters would separate them into individual sections. First, the volume of the gutter is calculated by:
Volume of a Concrete Gutter: Gutter Width x Length x Flag Thickness
Similarly, the volume of the curb is calculated by:
Volume of a Concrete Curb: Curb Depth x Length x (Curb Height + Flag Thickness)
Since the curb sits on top of the gutter, but the area underneath the curb is concrete, you will need to add the curb height on top of the flag thickness. The gutter flag thickness is usually slightly less than the pavement, to allow for water run-off to flow into the gutter. Inches are commonly used when measuring curbs and gutters. For example, the thickness of a gutter flag might be 9 inches, the gutter width might be 12 inches, and the curb height might be 4 inches.
How Much Does Concrete Cost?
The cost of concrete is commonly quoted in dollars per yards of concrete, however, they can also be priced by square footage. The average price per square foot for concrete is $6 per square foot.
Smaller projects might use concrete mix bags, which often come in sizes of 40 lbs, 60 lbs, and 80 lbs. Concrete would then be made on site. Larger projects might use a ready-mix concrete supplier, which delivers pre-made concrete directly to the project site with barrel trucks.
According to the Virginia Ready Mixed Concrete Association, the cost per yard of concrete is well over $100.