Yesterday, I learned the concept of ppi (pixel per inch), similarly there is ppcm (pixel per centimeter), and find that the ppi of my monitor is

  1. Then I become curious about how many pixel I have for each letter in my terminal.

I also have the question how big is a pixel in mind for a quite while, now I realized it’s not the right way to ask the question.

ppi is self-explained. Looking at my monitor resolution, it’s 1280 x 800, i.e. 1280 pixels in width and 800 in height. I am only interested in width for now, height is all the same. I found that a full line in my terminal contains about 180 letters. Assuming this 180 letters use up all pixels in width (actually this is an approximation, though I am aware some pixels are used by the border of the terminal window), this leads to

1280 / 180 = 7 pixels

which means each letter occupies 7 pixels in width. Of course this number depends on the letter (but if it’s mono spaced, it’s fine), the font, and the font size (11pt in my case), as well. For a given letter and font, the number increases as font size gets bigger.

Using ppi, I also found the size of pixel is

1/110 = 9.1^(-3) inches ≊ 0.02 cm = 0.2mm.

I was a bit surprised at this, a pixel on a regular monitor is actually quite big. I thought it would be invisible with naked eyes, but now if I look closer, definitely I can see the pixels, and even count them, I did that for letter T in my terminal, it’s around 7 +/- 1, so my calculation is right. The fluctuation is due to my burning eyes. I should not look at the screen so closely, but it’s around 7 for sure.

The pixel size gets even bigger when it comes to projectors. That’s for sure. When I was presenting stuff, I totally remember those squared dots when I come close to the screen.

Therefore, don’t ask what is the size of a pixel because it depends on the display. Ask for ppi instead, all right, it also depends on the display, but it is more of a standard way of asking such questions, and you can calculate the size of the pixel if interested easily with ppi.

Above is a little memo for my understanding of ppi.