The library science literature does not show a reliable way to calculate digital storage needs when digitizing analog materials such as documents, photographs, and sound recordings in older formats."Library professionals and library assistants who lack computer science or audiovisual training are often tasked with writing digital project proposals, grant applications or providing rationale to fund digitization projects for their institutions." Digital project managers need tools to accurately predict the amount of storage for digital objects and also estimate the starting and ongoing costs for the storage. This paper provides two formulae for calculating digital storage space for uncompressed, archival master image and document files and sound files.
Estimates from earlier sources:
- thirty megabytes of storage for every hour of compressed audio,
- one megabyte for a page of uncompressed, plain text (bitmap format)
- three gigabytes for two hours of moving image media
- 90 megabytes for uncompressed raster image files,
- 600 megabytes for one hour of uncompressed audio recording,
- “nearly a gigabyte of disk space,” for one minute of uncompressed digital video.
- 100 gigabytes (GB) of storage for 100 hours of audio tape
- These can be adjusted to alter both file size and quality, depending on the choice of digitization standard, the combination of variables used in a chosen standard and the quantity of digital storage required.
- As the experiments demonstrate, the formulae for still image and audio recordings are extremely accurate. They will prove invaluable to digital archivists, digital librarians and the average user in helping to plan digitization projects, as well as in evaluating hardware and software for these projects.
- Digital project managers armed with the still image and audio formulae will be able to calculate file sizes using different standards to determine which standard will suit the project needs.
- Knowing the parameters of the still image and audio formulae will allow managers to evaluate equipment on the basis of the flexibility of the software and hardware before purchase.
- Using the still image and audio calculation formulae in workflows will help digital project managers create more efficient project plans and tighter grant proposals.
- The formulae for calculating storage sizes: length of the original audio recording, sampling rate, bit depth, and number of audio channels.
- Formula for Calculating File Sizes of Uncompressed, Still Images:
One of the tables in the article on calculating file size and comparing to the actual size: