units in tex

tex-units.tex

\begingroup
\catcode`P=12 \catcode`T=12
\lowercase{\endgroup\def\removept#1.#2PT{#1\ifnum#2>0 .#2\fi}}
\def\strippt{\expandafter\removept\the}
\def\convertto#1#2{\strippt\dimexpr#2*65536/\dimexpr1#1\relax\relax}
\def\headertt#1#2{\bf #1}

\halign{\bf#\hfill &
  \quad\convert{#}{1pt}\hfil &
  \quad\convert{#}{1mm}\hfil &
  \quad\convert{#}{1cm}\hfil &
  \quad\convert{#}{1ex}\hfil &
  \quad\convert{#}{1em}\hfil &
  \quad\convert{#}{1bp}\hfil &
  \quad\convert{#}{1dd}\hfil &
  \quad\convert{#}{1cc}\hfil &
  \quad\convert{#}{1pc}\hfil &
  \quad\convert{#}{1in}\hfil \cr
\global\let\convert\headertt
    &pt&mm&cm&ex&em&bp&dd&cc&pc&in\cr
\global\let\convert\convertto
  pt&pt&pt&pt&pt&pt&pt&pt&pt&pt&pt\cr
  mm&mm&mm&mm&mm&mm&mm&mm&mm&mm&mm\cr
  cm&cm&cm&cm&cm&cm&cm&cm&cm&cm&cm\cr
  ex&ex&ex&ex&ex&ex&ex&ex&ex&ex&ex\cr
  em&em&em&em&em&em&em&em&em&em&em\cr
  bp&bp&bp&bp&bp&bp&bp&bp&bp&bp&bp\cr
  dd&dd&dd&dd&dd&dd&dd&dd&dd&dd&dd\cr
  cc&cc&cc&cc&cc&cc&cc&cc&cc&cc&cc\cr
  pc&pc&pc&pc&pc&pc&pc&pc&pc&pc&pc\cr
  in&in&in&in&in&in&in&in&in&in&in\cr
}
\bye