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0.02 cubic feet is a good average for one folder of materials, could use .01 for a very slim folder and up to .05 for a thick/expanded folder.

Extent calculator
The UNLV extent calculator is useful for calculating cubic footage of unusually sized boxes or adding extents made up of different container types.

Digital extent

Digital extent should ALWAYS be expressed in gigabytes at the highest level of description (collection-level for manuscripts, series-level or record group-level for archives).  Counts should be rounded to the nearest two decimal places, and values less than 1 should start with a leading zero (ex: 0.5, not .5).
Digital extent should be recorded in a separate element from the physical extent in the bibliographic record (add a second 300 field), in the Aspace accession record (add a second extent, portion="part"), and in the finding aid (add a second <physdesc>). 

Estimating digital extent for media:
If you are describing disks at the point of accession and you are not imaging the disks, calculate the estimated extent in gigabytes based on the maximum capacity of each piece of media:

  • 3.5 inch floppy disk (1.44 MB per disk)  =  0.01 gigabytes
    • 1    3.5 floppy disk  =  0.01 gigabytes
    • 10  3.5 floppy disks =  0.01 gigabytes
    • 25  3.5 floppy disks =  0.02 gigabytes
    • 20  3.5 floppy disks =  0.03 gigabytes
  • 1 DVD   =  4.7 gigabytes
  • 1 CD (700 MB)  =  0.68 gigabytes
  • Digital video  =  1 gigabyte for every 5 minutes of video. So:
    • Mini DV (83 minutes) =  16.6 gigabytes
    • DVCAM (124 minutes) =  25.3 gigabytes
  • Zip disks usually have the MB on them:
    • 100MB  =  0.1 gigabytes
    • 250MB  =  0.24 gigabytes
    • 750MB  =  0.73 gigabytes


    Example digital extent statements for unprocessed/unimaged media:
        0.01 gigabytes (1 3.5 inch floppy disk).
        4.71 gigabytes (1 zip disk and 1 digital video disc (DVD).

    Example of unprocessed electronic media accrual to processed collection (these would be coded as two separate 300s/extents):
        2 gigabytes (817 digital files, 10 digital folders).
 0.02 gigabytes (2 unprocessed 3.5 inch floppy disks).

Calculating actual extent:

If you know the ACTUAL gigabytes, either because 1) the electronic records were acquired as part of a server-to-server transfer or 2) you have imaged media either during accessioning or processing, provide the digital extent of the records on network storage.

If, during processing, you encountered media that you were unable to image successfully (ie imaging failed or media were determined to be blank), omit those from the digital extent rather than estimating the theoretical digital space they would/could take up. The unimaged media should naturally be included in the physical extent by virtue of taking up space in containers.

Calculate digital extent based on the Use Copies folder once all use files have been extracted from disk images and all "digital detritus" has been removed (system files, etc). Do this by right clicking on the Use Copies folder and selecting Properties. Record the total volume and contents of the Use Copies folder in terms of gigabytes (use the Size count rather than Size On Disk), number of files, and (if applicable) number of folders. Even if you know that some of the files are "unreadable" due to file corruption, lack of rendering software available, etc., record the total volume. If some media were not able to be imaged during processing, do not count these in the digital extent (since we keep the disks they will be represented in the physical extent).


If you have a disk image but have not extracted use files, for instance - a server transfer at the point of accession, use the volume of the disk image(s) as your digital extent.

When adding an unprocessed accrual of electronic records to an existing/processed collection, record the unprocessed volume separately (see example below).

    Example digital extent statements for extracted files on network storage:
        0.02 gigabytes (39 digital files, 12 digital folders)

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