Inch to Millimeter (in to mm)

Two fixed definitions drive every conversion on this page. A typographic point is 1/72 of an inch. A CSS reference pixel is 1/96 of an inch. That makes 1 px exactly 0.75 pt, and 16 px exactly 12 pt — which is why 16 px became the default body size on the web: it matches the 12 pt that print had already settled on.

A pica is 12 points, so 1 pica = 16 px. InDesign, Quark and most print workflows measure column widths and gutters in picas; CSS has no pica unit, so those measurements have to be converted before they reach a stylesheet. On this page, 1 in = 25.4 mm.

The CSS pixel is a reference unit, not a hardware pixel. On a 2× or 3× display, one CSS px still occupies 1/96 inch of visual space — the device simply renders it with more physical pixels. Converting CSS px to physical pixels requires the device pixel ratio, which is a separate calculation from anything on this page.

Metric print specs go through the inch: 1 in = 25.4 mm = 96 px = 72 pt. A 210 mm A4 page width is therefore about 794 px at 96 dpi — useful when matching a web layout to a printed one.