I have decided to convert from 4-drawer vertical filing cabinets to office shelving.  How many shelving sections will I need?
First we need to figure out the capacity of your existing filing system.  Then we will figure out how many office shelving sections you will need.

How to measure filing capacity: 
Capacity for filing systems is measured in linear filing inches or LFI.  LFI is the total number of usable storage inches in a filing system.  For example, if a drawer on a vertical filing cabinet's inside measurement is 25" deep, than that drawer's capacity is 25 LFI.  Or, if a drawer on a lateral filing cabinet measures 34" wide on the inside, than the filing capacity of that drawer is 34 LFI.  The measurement (width or depth) used to calculate LFI is always the direction the folders are stored.  The folders are stored left to right in vertical or office shelving systems, so the width is used to calculate LFI.  The folders are stored front to back in vertical filing cabinets, so the depth is used to calculate LFI.

Example system: 10 existing 4 drawer vertical filing cabinets converted to office shelving.
Each drawer in a vertical filing cabinet is about 25" deep.  Therefore, a four-drawer vertical cabinet will provide approximately 100 LFI (4 x 25).  Multiply the 100 LFI by the number of filing cabinets (10) and you get a total system capacity of 1,000 LFI.

Office shelving sections come in many sizes.  For this example we will use a 48" wide office shelving section with eight usable shelves.  Each shelf will hold approximately 46" inches of files for a total of 368 LFI per section.  How many shelving sections will we need to hold the existing 1,000 inches of files?

We will need only 3.  As we stated above, each office shelving section provides 368 LFI.  Three sections will provide you with a total of 1,104 LFI which will more than accommodate the folders from your existing filing cabinets.

Space Savings:
In addition to speeding up folder retrieval times, end tab office shelving will also save you space.  In the example above the vertical filing cabinets will take up approximately 26 square feet while the office shelving will take up only 12 square feet.  

Conclusion:
With office shelving, you will get a greater folder storage capacity in less than half the space, when compared to lateral filing cabinets.