A measurement for the number of characters of a particular size and font that can fit into a line one inch long. This number is affected by the type抯 point size and the width of the letters in the fontbeing measured. In monospace fonts, every character is the same width, so figuring out the number of charactersper inch is a simple task. In proportional fonts, characters have varying widths, so the number of characters perinch must be calculated as an average of the different widths.