What does 5 mm look like?

That depends what you want to convert it to. Among other things, that's equal to 0.5 cm, and to 0.005 meters.

The most popular SI conversions are: 5mm is 0.005 metres, 0.000005 km, 5000 microns, 5000000 nanometres, 50000000 angstroms, 5000000000 picometres.