Digital Project Guidelines and Information : Formula for Calculating Uncompressed Image Size

This page last changed on Apr 02, 2012 by prescott.

DPI=dots per inch (in this use it is synonymous with PPI which stands for pixels per inch)

The formula for calculating uncompressed image size in bytes is:

  • ((DPI x height in inches) x (DPI x width in inches) x bit depth) divided by 8.
    • Multiply the DPI with the height of the image
    • Multiply the DPI with the width of the image
    • Multiply the results of the two calculations - this gives you the total number of pixels
    • Multiply the result with the bit depth of the image, which is the number of bits per pixel
    • Since there are 8 bits to a byte you divide by 8 to get the bytes.
    • There are 1,048,576 bytes in a megabyte (not exactly a million, but close)

Example: If you have an image that is 11 x 14, and is imaged at 600 DPI/24 bit (depth)

    • 600 x 11 = 6600
    • 600 x 14 = 8400
    • 6600 x 8400 = 55,400,000 pixels
    • 55,440,000 x 24 = 1,330,560,000
    • 1,330,560,000 / 8 = 166,320,000 bytes
    • 166,320,000 / 1,048,576 = 158.615...

      This uncompressed file would be 158.6 megabytes

Classification of digital measurements

Processor or Virtual Storage
Disk Storage
1 Bit = Binary Digit1 Bit = Binary Digit
8 Bits = 1 Byte8 Bits = 1 Byte
1024 Bytes = 1 Kilobyte1000 Bytes = 1 Kilobyte
1024 Kilobytes = 1 Megabyte1000 Kilobytes = 1 Megabyte
1024 Megabytes = 1 Gigabyte1000 Megabytes = 1 Gigabyte
1024 Gigabytes = 1 Terabyte1000 Gigabytes = 1 Terabyte
1024 Terabytes = 1 Petabyte1000 Terabytes = 1 Petabyte
1024 Petabytes = 1 Exabyte1000 Petabytes = 1 Exabyte
1024 Exabytes = 1 Zettabyte1000 Exabytes = 1 Zettabyte
1024 Zettabytes = 1 Yottabyte1000 Zettabytes = 1 Yottabyte
1024 Yottabytes = 1 Brontobyte1000 Yottabytes = 1 Brontobyte
1024 Brontobytes = 1 Geopbyte1000 Brontobytes = 1 Geopbyte