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How to Calculate PPI

PPI stands for pixels per inch and is a measurement of image quality. It is used when printing photos or other images from a computer. Three hundred PPI is considered a high quality image, while less than 150 PPI is indicative of a poor quality image. The actual image quality when you print will also depend on your printer. To calculate the PPI of your printed image, you will need to know the dimensions of your image in pixels and how large you plan to print the image.

Instructions

- 1
  Multiply the length of the image in pixels by the width of the image in pixels. For example, take an image that is 800 pixels by 600 pixels that will be printed out at as an 3 inch by 5 inch print: 800 pixels multiplied by 600 pixels equals 480,000 pixels squared.
- 2
  Multiply the length and width of the final size of your image in inches. This is the area in inches of the final print. Continuing the example, 3 inches multipled by 5 inches equals 15 square inches.
- 3
  Divide the result from Step 1 by the area in the final print. For the example, 480,000 pixels squared divided by 15 square inches equals 32,000 pixels squared divided by square inches.
- 4
  Take the square root of the result from the previous step. This will give the PPI for the print. The example print will have a PPI of: sqrt (32,000 pixels squared divided by square inch) equals 179 PPI.

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