Working with the Libraries on preserving digital materials

It can be difficult to accurately estimate the amount of storage space needed for a digital project. However there are some tools that you can use to help develop an estimate for certain types of materials when needed for completing a grant application and/or discussing preservation needs with the Digital Preservation Repository Technology Department.

Digitized images

To calculate the estimated space needed for storage of digitized uncompressed images the formula provided below can be used. It will require knowing the size of the original image and the resolution and bit depth that will be used. The resolution will depend on the size of the items being digitized and the bit depth.

Some samples of ‘best practices’ to determine suggested resolutions MDL:

• Minnesota Digital Libraries, Digitization Best Practices (https://mndigital.org/standards-best-practices/best-practices-digitization)
• MNHS: ??
• FADGI: Federal Agencies Digital Guideline Initiative (draft 2022)

Formula to calculate size

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Born digital images

• If new images will be taken from a known camera, you can estimate file sizes by taking sample images that would be similar to those for your project. Use the same settings you expect to use for the project.
• Review the file size of the images taken and extrapolate based on the number of images you expect to take and/or preserve.
• Image file size average from sample images X the number of expected images = approximate total size of storage needed in [whatever unit you used]

The size of audio files can be calculated when the following parameters are known: bit depth, sampling rate, duration of audio, and number of channels. This estimate does not include any metadata and assumes the file is uncompressed.

• The following formula is used to calculate the estimated size of the audio file:
  • 
• Use the converter listed under helpful resources to convert Bytes to a more appropriate value
• Some sites that do this calculation for you include:
  • Colin Crawley’s Audio File Size Calculator
  • Omni Calculator’s Audio File Size Calculator

Size Conversion Tool

• What’s a Byte
  • use to convert bytes to megabytes or gigabytes etc (uses 1024 for more accurate results, not 1000 like others do)