Convert pt (postscript/PDF unit) to inch or mm in Javascript

Here are some simple utility functions to convert the preprint unit pt (defined as 1/72 inch) into inches or mm.

function convertPtToInch(pt) { return pt / 72; }
function convertInchToMM(inch) { return inch * 25.4; }
function convertPtToMM(pt) {
  return convertInchToMM(convertPtToInch(pt)); }

// Example usage
console.log(convertPtToMM(595)) // Prints 209.90277777777777

Note that while this conversion is exact, there is some tolerance required when comparing these units: An ISO A4 paper is defined as 210x297 mm - or 595x842 pt.

However, converting 595x842 pt into mm results in 209.902777 mm and 297.038888 mm respectively. Watch out for those tolerances if you try to compare paper sizes. I recommend a tolerance of at least 0.25 mm.