[majewsky]

I have

  alias units='units --verbose

in my shell rc which makes the output much more understandable:

  You have: mph
  You want: kph
          mph = 1.609344 kph
          mph = (1 / 0.62137119) kph

[xigoi]

I find the reciprocal thing useless, so I have units='units --compact --one-line', which gives just the number you want.