The tenth planet is about 930 miles (1,500 kilometers) across, according to Mike Brown, an astronomer at the California Institute of Technology, who led the U.S-based team who announced the discovery of the planet.

The tenth planet, 2003-UB313, will be visible over the next six months and is currently almost directly overhead in the early-morning eastern sky, in the Cetus constellation.
It lies nine billion miles from earth so you would need a very powerful telescope to view it, such as the 48-inch Samuel Oschin Telescope at Palomar Observatory.

The new 10th planet is tentatively being called 2003-UB313. The object was originally discovered in 2003, but its status as a planet was only determined this year. As astronomers detected that it was rotating around the sun, they realized that they had discovered a previously unknown planet.
According to Mike Brown, a [...]

In the outer regions of our solar system, an object bigger than Pluto has been discovered and has now been designated as our tenth planet! This site, www.tenthplanet.info will chronicle the discovery of this planet, and will hopefully serve as a learning resource for future generations to come.