Commercially available citrus trees will be labeled as "dwarf" if they're on root stock which can limit growth.

That said, "dwarf" trees are seldom as small as people wish for.

Ok thanks. Does anyone know what specific varieties of rootstocks are commonly used?

The only dwarfing rootstock for citrus is the 'Flying Dragon' form of Poncirus trifoliata. It is suitable for most citrus varieties.
However, if you are growing in pots rather than in ground, the pot size is as much the limiting factor as rootstock selection.

It also depends on the vigor of the variety being grafted. As a rule of thumb, you can figure that any variety grafted onto 'Flying Dragon' at 18-24" AGL will be about 50% or a little smaller than the same variety growing on its own roots. So a 16' tree will be dwarfed to about 8' and a 30' tree will be dwarfed to about 15'. It will also survive about 8-10 degrees colder temperatures than self-rooted varieties.

I would like to read up on that being 8-10 degrees cold hardier. Can you give me the source of that info? I am very interested in that.
Thanks