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How to Calculate the Area of a Scanned Image

The old photograph you scanned explodes on the screen, appearing many times larger than the original. Predicting the area of the scanned image may pose a challenge unless you take note of a scanning parameter called DPI or PPI (dots or pixels per inch) that is often referred to as the scanner resolution. This parameter determines how much detail from the original image is stored in the scanned, digital image. The higher the DPI value, the larger and more detailed the scanned image will be.

Ruler
Calculator

Instructions

- 1
  Use a ruler to measure the physical dimensions (width and height), in inches, of the original image on the paper.
- 2
  Read the DPI or PPI resolution setting for the scanner from the scanner console or scanner properties window in your image scanner software. Note that some scanner software may use the word "resolution" instead of DPI or PPI to refer to the scanner resolution.
- 3
  Multiply the physical dimensions by the scanner resolution to obtain the digital dimensions in pixels. For example, a physical 8.5-by-11-inch image scanned at a resolution of 300 DPI or PPI would produce a digital image 2550 pixels by 3300 pixels.
- 4
  Multiply the width in pixels by the height in pixels to obtain the area (in pixels squared) of the digital image. For example, an 8.5-by-11-inch image scanned at 300 PPI would produce a 2550 pixels x 3300 pixels image, which covers an area of 8,415,000, or 8.4 mega square pixels.

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