Stylus font functions. Add this to a vars.styl file that you would import all over the place.

stylusfontconversions

//========== root values
phi = 1.618
fi = .618
golden = 1.61803398875

rootPx = 16px
rootEm = 1em
rootPercent = 100%
rootPt = pxToPt(rootPx)

//========== font functions
hifi()
        unit(phi, 'em')
lofi()
        unit(fi, 'em')
rem(n)
        rootEm * n

pxToPt(n)
        unit(.75 * n,pt)

ptToPx(n)
        ceil(unit(n * 1.333333333,px))

ptToEm(n)
        unit(ptToPx(n) / rootPx,em)

emToPx(n)
        unit(n * 16,px)

pxToEm(n)
        unit(n/rootEm,em)

emToPercent(n)
        (n/rootEm)%