A pt is 1/72 of an in, and a px is 1/96 of an in.

A px is therefore 0.75 pt [source].

In CSS, everything is somewhat abstracted, so a unit such as a "pt" is not necessarily one point in physical size, especially on a screen, an "in" is not necessarily one inch in size, and so forth. Even a "px" is no longer necessarily one pixel in size anymore. In CSS, everything is scaled to be consistent with a virtual 96 ppi device viewed at normal reading distance. On screens and pixel-based devices that differ significantly from 96 ppi or which aren't read from normal reading distance, the px unit will be scaled by some factor, and all other units maintain the same relationships to it accordingly - that is, an in unit will still be 96 px units, and a pt unit will still be 1/72 of the in unit.

In print

In print, a point was traditionally somewhere from around 1/67 of an inch to 1/72.5 of an inch.

In digital mediums, it has become a de-facto standard for a point to be exactly 1/72 of an inch nowadays, though there are still alternative measurements in less common use which vary slightly from 1/72, but not by much.

In print, you don't usually measure in pixels, because they are a technical detail about the target printer or device that are not an absolute measurement. For instance, a design may be printed at 125 dpi, 300 dpi or at 1200 dpi and still be the same physical dimensions.

Point vs Pixel: What is the difference?

Is a CSS pixel really an absolute unit? That is, is 1 inch = 96px true?