Formula How to Calculate Weight for I-Section

Look in tables, saves calculating

Density times volume.

Which one, they are not all the same? W's are rolled differently than S's and thus have different formulas. W = Wide Flange, S = Standard.

Which one are you looking for specifically? (hopes they respond with something like 'S3x5.7')

'S' type

Cool, easy enough.

ALL Standard I-Beams are rolled to a strict set of manufacturing standards which every steel mill MUST conform to. In the case of these items, it's ASTM A36.

This standard requires that the cross-sectional area, angles, and radii of the structural shape are consistent. For those structural shapes that have angles in their profile, and are also purposed for load-bearing (C-channels, Beams, T's) the standard acknowledges that the weight of the items are an important consideration but is also not easily derived due to the angles and radii. Therefore the standard requires the 'Weight-per-Foot" be included in the product designation.

Where you can order rectangular tubing by specifying HxWxWall, you cannot order a beam by specing HxWxWeb Thickness. Well, I guess you could but the supplier would scratch their head and rewrite your spec to HxWpF.

Thus, the formula to calculate the weight for a S7x15.3 Standard I-Beam is 15.3xLength in Feet.

Now, if you want to derive your own formula, you will need to obtain the cross-section dimensional limits of the shape, which are not commonly published so you'll have to do some digging.

Once you calculate the surface area of the shape's cross-section, the other components of the formula will be length and density, as in Area x Length = Volume, then Volume x Density = Weight. A good standard density for low-carbon steel is 0.2833 lbs per in^3

My advise though, don't. It is an unnecessary investment of time considering ALL shapes of this nature account for the difficulty in determining cross-sectional area and included their weight in their description.

GA, most A36 structural steel will be listed in a table and have the weight per foot listed as part of the item description.