New Sprayer cordless

I really like this and the price. Only thing is I am concerned with the capacity. 1.3 g
I am thinking I would be filling it up before i finish an average house.
How much on average in RTU would you think is used for each house? I do a lot of 3 and 4 rooms jobs. I just don't know if this would do the job at 1.3g

http://www.mastercleanstore.com/Sigent-400B-Cordless-_p_118.html