For the do-it-yourself homeowner concrete projects can pose a very unique problem. A very small project can normally be easily handling with a bag or two of ready mix concrete. When the job becomes larger, such as an entire new driveway, it is time to order concrete from a commercial supplier. The intermediate jobs, too big for ready mix yet too small to require a truck load of concrete, can present a problem. If your project will only require one or two yards of concrete many commercial suppliers will be hesitant to help, or the cost will be too high for such a small amount of concrete. Therefore, it is imperative you first know the exact amount of concrete your job will require.
Calculating Your Concrete Needs
Lay out your entire project, either by using stakes and string on the ground, or on paper. You will need to know how many square feet of surface you intend to cover. For this calculation take the length times the width, measured in feet. For example a ten foot by eight foot patio will be calculated 10 x 8 = 80 square feet.
The next step is to calculate the cube of the area you are covering. For a patio a slab thickness of four inches should be more than adequate. For this calculation you can use one of two methods. Four inches is equal to one third of a foot, so you multiple .33 x 80sq.ft. = 26.4 cubic feet.
The other method is to convert everything to inches. Your formula will now look like this, 120” x 96” x 4” = 46,080 cubic inches. A cubic foot is 12” x 12” x 12” which equals 1,728 cubic inches. To get the cubic feet divide 46,080 by 1,728 and you get 26.6 cubic feet.
Calculating a Cubic Yard of Concrete
Concrete, when delivered by a concrete truck, is sold by the cubic yard. A cubic yard of concrete is three feet high by three feet wide by three feet deep. 3’ x 3’ x 3’ = 27 cubic feet in a cubic yard. For the project listed above you needed 26.6 cubic feet of concrete which is just slightly less than one cubic yard.
Finding a concrete supplier who will deliver just a single yard of concrete may be difficult. In some instances the supplier may have a large job nearby you and they will supply you with a yard of concrete left over from that project, for a price of course. If they have no other projects in your area, the cost of delivering a single yard of concrete makes it rather unattractive for them.
Slightly Larger Projects
When working on a larger projects you will find suppliers much more willing to work with you. A new driveway for instance could measure as much as twenty feet wide and forty feet in length. This project, poured at a depth of four inches would require nearly 267 cubic feet of concrete. (20’-0” x 40’-0” x 0’-4”) This number divided by the cubic feet in a yard of concrete will give you the number of yards required. 267 divided by 27 = 9.88 cubic yards. For this size project you should have no trouble finding a concrete supplier willing to work with you.
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