Garden retaining wall

[Moonshine]

I have a garden wall going in to separate a level of about 600-800mm. It's going to be stone faced.

Any idea on depth of footing typically needed and width of wall? 

I am thinking block behind the stone

[Mr Punter]

It is more the width of the footing.  Extend it by at least 400mm on the low side and use some starter bars with hollow blocks, concrete filled.  Add some weep holes low down.  800mm is no a lot but better done properly.