I cannot think of the last time that anyone I know or have heard in
conversation or who asked me directions ever used the full name. People
just call it Kings Cross - after the area.

Once there people may ask the way to St Pancras station.
--

Well, to be fair it'd be quite a mouthful to say the whole lot, but it's
useful to have the station named on the map for people looking for it. This
will be even more true when St Pancras leapfrogs King's Cross in importance
when the Eurostar, Javelin and Thameslink trains all go to St Pancras.

And to be nit-picky in a friendly and hopefully informative way, the area is
really St Pancras, not King's Cross! The name King's Cross technically
applies only to the junction of Euston Road with Pentonville and Gray's Inn
Roads and York Way (the King's Crossroads), and the station itself. The area
was the Battlebridge part of St Pancras, which was listed in the Domesday
Book 800 years before King's crossroads was so identified.