How to Determine a Steel Beam Size

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The size of steel beams chosen in residential and commercial construction projects is critical to the integrity of the structure they are being used to build. The most common type of steel beam used in construction is the I-beam, which is also known as an H-beam or W-beam. I-shaped beams are effective at carrying bending and shear weight across their centers. It’s easy to select the right size I-beam for your project when you know the load, or weight, that you need the I-beam to bear.

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Measure the distance in inches that you need the steel beam to fill. Write this figure down on a sheet of paper as your clear span for the beam.

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Measure the length in inches of the floor joist that the I-beam must support. Divide that number by two. Write this figure down on your paper.

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Determine the vertical load for the beam. Write down “62” if it is supporting a one-story building; write down “124” if it is supporting two stories. Write down the specific load figure if the beam must support more than two stories worth of weight.

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Use a calculator to multiply the clear span by the length of the floor joist by the vertical load. Divide the result by 1000 to get the figure in KIPS, a non-Si unit of force equal to 1,000 pounds-force and understand that 1 KIP is equal to 4448.222 newtons.

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Use the attached chart (References 1) to find the width of steel beam that’s appropriate for your KIPS calculation. Locate your clear span in the far left column and look across and down to the right until you find your KIPS figure. Look up to the top row to see the width of steel I-beam, or size, that you need for your project to support the KIPS that will bear down upon it.