The mass of Kuiper belt has been estimated as 2% of the mass of the Earth. This is based upon 800,000 positional observations of planets and spacecraft. The total mass of the Kuiper belt is two orders of magnitude larger than the mass of the Main asteroid belt.
It is almost three orders of magnitude smaller than the mass of the proposed 9th planet. The 9th planet is 10 times the mass of the Earth.
The 9th planet is calculated to be 800 to 1100 AU away. The Kuiper Belt is mainly concentrated around 39 to 49 AU.