How this calculator works
Pixels per inch is the number of image pixels that fit in one physical inch. Dividing a pixel count by that density gives inches, and multiplying inches by the density gives pixels. The value describes a print or a display only when the physical output size is known: the same 3,000 pixel image can be 10 inches wide at 300 PPI or 30 inches wide at 100 PPI.
Formula
inches = pixels / pixels per inch. pixels = inches x pixels per inch. pixels per inch = pixels / inches.
Worked example
3,000 pixels at 300 PPI is 10 inches. At 100 PPI the same image is 30 inches wide. A 1,200 pixel wide image printed at 300 PPI is 4 inches wide.
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Frequently asked questions
Is PPI the same as DPI?
PPI describes image pixels per inch. DPI describes dots of ink or toner per inch in a printer. Printers often use several ink dots per image pixel, so the numbers are related but not identical.
Does an image file have a physical size?
Not until a density and an output size are chosen. A pixel grid has no inherent inch size, which is why the PPI value must come from the print or display specification.
Why is 72 PPI sometimes mentioned for screens?
Older Macintosh screens used about 72 pixels per inch, so 72 PPI became a convention for web images. Modern screens vary widely, and CSS pixels are a logical unit rather than a fixed physical size.