Measuring for concrete is a relatively easy procedure, based on a simple volume calculation. Do not be intimidated by measuring for concrete steps or stairs. The steps are essentially different concrete slabs built one on top of the other. When viewed like this, they become easy to separate and measure when you are still in the planning stages.
Measuring First Step

Measuring the first step will probably be the hardest part of finding out how much concrete you need. Measure both the width of the step to find out how far across it is as well as the depth or how far the step goes in, all the way to the base or foundation the stairs will be stopped by. Measure the height of the first step (all your steps should be the same height), and you can multiply them together, in inches, for a basic volume equation. For example, the first step may measure 20 inches wide, 36 inches in, and 6 inches high. Multiplied together, they would equal 4,320 cubic inches. This may seem like a lot, but you can convert to feet later.
Measuring the Other Steps

After the first step is done, you can either measure the other steps the same way, or measure the space that the steps retract from the first step and subtract that space from the original volume formula, whichever is easier. The smallest steps retract about 6 inches per step, but you may want more for a more comfortable stair tread. If you subtracted a space 8 inches deep from the volume of the step in the first section, you would get 4,320  960, or 3,360 cubic inches, which you would add to the total for both steps. Once you have each step measurement, add them together and convert the volume to feet by dividing by 1,728, or 12 x 12 x 12. If you only have two steps, then 4,320 + 3,360 = 7,680, which divided by 1,728 would be about 4.5 cubic feet.
Including Other Surfaces

Do not forget to include the other concrete surfaces involved in making your stairs when you calculate the volume. You might be planning on a base slab in the ground before the stairs begin. If the steps are leading up to a patio, you will need to measure this patio area as well. Combine all the volumes together to get a final amount for the entire project.
Bag Yield

With a total cubic feet in mind, you are ready to buy bags of concrete. A normal 80pound bag of concrete equals about 0.6 cubic feet, which provides a useful reference. No matter the size of the bag, it will give an equivalent cubic feet of concrete produced that you can judge amounts by. Try to purchase a little more than you need to allow for unforeseen circumstances.
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