What is the difference between pixel pitch and pixel density?

Question

This site already has a question around what is pixel density, but it doesn't mention pixel pitch at all. I am wondering what the relationship is, and what is important about the relationship to photographers today.

Not to foil the answers from others, but this fun equation is what spurred the question:

pixel pitch = 1/sqrt((pixel density per cm^2)/(10000^2))

I have no idea really what the above equation means, or even if it is accurate. I found it at this thread at dpreview.com.

user2719 · Accepted Answer

It's just a reciprocal relationship. Where pixel density measures, say, the number of pixels per inch, pixel pitch measures the number of inches per pixel (or the center-to-center spacing between pixels).

Pixel pitch expressed as a linear measurement, and if the pixels are non-square you may see two values specified. Pixel density, on the other hand, may be expressed as a linear measurement (pixels per inch or millimeter or what have you) or as an area measurement (pixels per square inch or pixels per square millimeter) -- your equation assumes an area measure of pixel density and square pixels, and converts to a linear value.

I should probably add that pixel pitch is usually used to state device specifications (screens or sensors) -- you wouldn't often see it used to describe, say, the resolution settings you used to print an image.

Monitorer · Answer

Avoiding too much complexity, e.g. for monitors, Pixel Pitch is the distance between 2 pixels, measured in mm. We know that it takes 25.4mm = 1inch and pixel density is pixels per inch. So to calculate what is the pixel density given the pixel pitch, here is an example:
What is the pixel density for a monitor with Pixel pitch = 0.1554mm?
Answer: 1/0.554 * 25.4 = approx 163
Just work backwards if you're given the pixel density.

What is the difference between pixel pitch and pixel density?

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