How to Calculate Irregular-Shaped Concrete Yardage

Concrete
Concrete (Image: concrete wall image by Lela Obradovic from Fotolia.com)

Building a concrete slab or pouring your own concrete pathway can be a fun but challenging weekend project. Once you have figured out where you want your concrete slab or path, the next step is to calculate the amount of concrete to purchase. Concrete is solid in cubic feet: Normally you would multiply the length x width x height to find the volume; however, if you have an irregular shape, you are going to need to take an additional step or two to calculate the correct amount of concrete.

Things You'll Need

  • Measuring tape
  • Paper
  • Pencil

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Draw a rough picture of the area you want to pour concrete into. This does not have to be to scale.

Break your picture up into regular geometric shapes like squares and rectangles. For example, an L-shaped plot can be broken up into one square and one rectangle.

Number the individual shapes on your diagram. For example, if you have three rectangles, label those rectangles 1,2 and 3.

Measure the length and width of the first shape, and then multiply these measurements together. For example, if your first rectangle is 4 feet by 2 feet, then 4 x 2 = 8.

Measure the depth of concrete required, in feet. For example, you may want to have a concrete slab that's 1-1/2-feet deep.

Multiply Step 4 by Step 5. For example, 8 x 1-1/2 = 12.

Repeat Step 4 to Step 6 for all shapes you identified in Step 3.

Add the results from all your shapes together. For example, if you have three shapes that equaled 12, 10 and 8: 12 + 10 + 8 = 30. This is your yardage in cubic feet.

Tips & Warnings

  • If you have a triangular section in Step 6 or 7, multiply the length by the width and divide by two to get the area for a triangle.
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