How Much Concrete Do You Need?

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Concrete Calculator Formula

What formula should I employ to figure out the amount of concrete I’ll require?

How to calculate concrete?

  1. Decide on the thickness you would like the concrete to be.
  2. Take measurements of both the width and length you’d like to be able to
  3. Multiply the length by width to determine the square footage.
  4. Convert the thickness of inches to feet.
  5. Multiply the thickness of feet with the square footage of the area to get cubic feet.
  6. Convert cubic feet into cubic yards, by multiplying it by .037

Here’s the math for a 10′ to 10′ patio made of concrete

  1. 10 by 10 equals 100 sq. feet
  2. 4 / 12 = .33
  3. 100x .33 equals 33 cubic inches
  4. 33 x .037 = 1.22 cubic yards

In essence, you’re looking for the volume of a space and changing it to cubic yards. Concrete volumes are calculated length wide x width.

To determine the number of bags of concrete you’ll require, divide the amount of cubic yards required by the amount of concrete you will need.

The following yields are for bag size:

  • 40 pound bags yield .011 cubic yards
  • 60 pound bags yield .017 cubic yards
  • A bag of 80 pounds yields .022 cubic yards


Do I need to order concrete in the yards from a Ready Mix firm or should I just buy bags?

For larger projects, such as driveways, they can be completed more easily by purchasing concrete per yard, instead of mixing bags after bags by hand. For smaller projects, like the walkway, modest footings or patio it is recommended to calculate the amount of concrete bags you need instead.

Concrete bagged is perfect for:

  • Small slabs of concrete to be used to be used as patios or sidewalks
  • Posts to fence posts or mailboxes
  • Repairing the foundation wall, pathways, or steps
  • Installing steps, small curbs or ramps
  • Decking, pergolas, footings, walls, and more

If you’re buying bagged concrete you might be able to get it delivered, but if it’s just one bag, you’ll need to transport the concrete yourself. Also, you’ll require additional equipment to mix the concrete. A mixer that you rent can be beneficial, but the wheelbarrow is only needed for the weight of a couple of bags.

Ready-mixed concrete in the yard is ideal for:

  • Large patios, driveways decks for swimming pools, and much many more
  • Foundation slabs for houses
  • Commercial sidewalks, parking lots, or parking lots.

If you’re looking to purchase concrete through a ready mix company They’ll require the quantity of concrete they need to deliver. Most ready mix companies require a minimum order of one yard and may charge shortage fees for partial batches. The typical truck can hold about 9-11 yards. If your project requires more concrete, several trucks will be required.


Atlanta Brick & Concrete in Atlanta, GA Figure Site

Calculating the amount of concrete required to make slabs (including strange forms)

Rule of rule of thumb: add 14.” on top of the width the slab to calculate the cost of concrete for your slab. This assumes that you have the job graded evenly to the proper depth and the grade is compacted.


If you look at your grade and find that one place is 4″ and some spots are 4.5″ or 5″-the most effective solution for both the quality of your work and your budget for concrete is to repair the grade.

odd shapes Convert oddly-shaped shapes to rectangles and odd shapes that are immediately easy to identify.

Imagine a driveway that measures 14′ by 20′ and your estimation will be accurate. This is the reason the driveway measures 16′ on its top, and is 12 on the lower part. Through the middle, the width is 14′ on average..

Calculating the quantity of concrete required to build footings

Footings are not always able to conform to the drawings exactly. In the case of rocky soil, the footings can fall apart when large stones are removed


It was intended to be the size of a 12″*12″ base, however notice how the left side of the footing is been sunk. Determine the size.

The excavator might have dug too deep or it might have rained and footings required to be dredged out further to get hard soil. It is therefore important to examine various areas on your footing to find an average size. Use the calculator to determine the amount of concrete you will need.

House slabs with 8″ above grade and the 4″ slab have a bit of the footings above the grade as well.

The footing is 12″ 12″ footing has to calculate 12″ 16″ which means that the footing must be calculated to be over the grade in order to reach four” slab’s slab’s thickness.



Estimating concrete steps

The steps may be difficult to determine however they are not. When there’s three steps leading to the porch:

  • Utilize the slab calculator in order to calculate the amount of concrete required to build the porch’s surface.
  • Use the footing calculator determine the sides of your porch as well as the steps.

Here’s an example:

The porch is 9 square. feet of porch area Enter in your slab calculation 4″ thickness, followed by 3′ width and 3 length. The result is .11 cubic yards.

The porch also includes 9 linear feet that are the 6″ step. Enter in the footing calculator the 6″ thickness in the 12″ width (always take steps in a figure with twelve” length) by 9 length. It’s .17 cubic yards.

The concrete required for the 3′ x 3 front porch would be .28 cubic yards. (.11 + .17 cubic yards = .28 cubic yards)

Repeat this process for further layer of the steps.

3′ x 3′ Porch


Estimating the quantity of filler base

Utilizing the Margin of Safety: Problems Caused by underestimating the amount of Concrete

Do not attempt to get the exact amount of concrete. Add a margin of security.

A well-placed order of concrete will complete the task with only a tiny amount left. The 20 cubic yards concrete order with 1 cubic yard left is a good choice. If a 20-cubic yard purchase is with a cubic yard deficit is not a good deal.

Extra cost of running short of concrete

  • Time off for crew members
  • A fee for short loads from the supplier of ready mix
  • A cold joint may be a problem (where one pour has ended and another one began)

Three steps to order enough concrete

  • Make use of the concrete calculator
  • Figure widths and depths in relation to how they were constructed at the location, and not just what the plans state.
  • Create a safety margin

The rule of thumb for determining the Margin of Safety:

When your purchase This much more
1-5 cubic yards .5-1 c.y. additional
6-10 c.y. 1 c.y. Extra
11-20 c.y. 1-1.5 c.y. additional

It is a bit of a sour taste to be left with additional concrete. You have the expense of this concrete, after all. But you should realize that you’re doing your part by purchasing enough concrete that means you’re likely to have some concrete left.

Inviting the ready-mix supplier you use to come visit your website

Once you’ve chosen the Ready Mix Supplier, have someone from the company visit your location to provide an opinions on the quantity needed. Compare the number with the one you have calculated. Discuss any deviations with the provider.

The ready-mix provider is vital to verify your perception of the job’s conditions, assessing your safety margins and spotting issues that you might not have considered and informing you about any local hazards you need to be aware of.

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