Height of NL grown 12/12 under 400watt hps?

I've got some Northern Light seeds and some Skunk + Haze (Nirvana) seeds germinating right now. If I use my DWC set up I've got exactly 2 feet of clearance under the light for the plants to grow.
How tall are these gonna get in a 12/12 grow under a 400watt hps?