Facility Planning: Methods for Calculating Collection SizePart 7 of the Facility Planning Series by Karen Watson & Robert Hubsher
In our last article we discussed weeding your collections and the importance of, and how to, measure your weeded collections. This topic is an important one and has another aspect that we address here.
You will find many articles and documents that advise the reader on ways to mathematically calculate collection size. These methods for calculating collection size serve as a backup or reaffirmation of the measurements you have taken at your library after weeding. We suggest two methods, for their ease of use and understandability (see examples below).
Once you have determined your current collection size, remember to add the 10-25% of unoccupied shelf space, for ease of access and to accommodate the anticipated growth of the collection for at least ten years.
Two Methods to Calculate Collection Size:
EXAMPLE ONE: Components Approach
Number of Items Method
50,000 items in the collection
Note: You can use the total collection size to get an estimate of the square footage required by using the Workform included in this article. It allows you to break the collection down by format (books, face out displays, reference books, periodicals, non-print materials) for a more accurate estimate.
The link to The Workform for Estimating Space Requirements Using the Components Approach, Number 5 of the 7 appendices in the ‘The Library Development Guide #5, 2010’ is as follows: Making the Case for a Building Project
EXAMPLE TWO: actual measurement
Linear Measurement Method
50,000 items in the collection
Note: The linear feet required to house the collection derived by this method will be used by your design professional to calculate the square footage required to house your collection. In order to do this, the design professional will need to know the height of your shelving units and number of shelves per unit. This method will provide a more accurate assessment of the space required to house your collections.
Keep in mind that if you choose to display some of your materials with the covers facing out, you will need to adjust your shelving requirements: a six shelf bay with one shelf allocated for face out display will reduce your available shelf space by 17% per bay (for a 5 shelf bay it is 20%; for a 4 shelf bay it is 25%).
Space allocation for shelving is also affected by the height of the shelving units. For example, a seven foot high shelf with six shelves 12 inches apart provides approximately one third more linear feet than a five foot high unit with four shelves. The higher the shelving units the less floor space required to accommodate the collections. The goal should be to accommodate the broadest range of accessibility across the full range of user mobility and height. In this context, general guidelines recommend that adult materials be shelved no higher than 60 inches (5 feet) and material for children be shelved no higher than 48 inches (4 feet).
You will discover that your designer will check your calculations, shelving counts and measurements. Be prepared to review these numbers very carefully.
Electronic and digital resources are an important part of a library’s collections. These resources do not occupy physical space. However, the hardware required to store, cool and/or provide access to the electronic databases and catalogues at public access computer workstations resides in the central computer room. Ensure that you have accurately estimated the size requirements for these ancillary rooms.
Click here to read Part 6 of this series.