In order to get (W) you have to figure your area that this beam is holding up. This is usually given in square feet. Then you need to know how many pounds per square foot the intended load will be. If you know these numbers then multiply the load per square foot by the number of square feet and that will be the total load on the beam.
You may consult your local building dept/official to get the code for your area for loads by the square foot. They should be able to tell you how many pounds per square foot for loads based on the use of the area, that is second floor sleeping area, first floor, storage, roof load, etc.
One good source for understand loads and load paths is the "Gravity Load Paths and
Residential Wood Structural Design-A Beginner's Guide, at
www.beamchek.com or
Click here for link to BeamChek.com go to the Publication page and read or download the pdf guide.
To get the Fb of any timber you have to know the type, grade and/or size.
Good luck.
Jim Rogers
