Officially recognised dwarf planets in our solar system

          There are 5 officially recognised dwarf planets in our solar system, they are Ceres, Pluto, Haumea, Makemake and Eris. With the exception of Ceres, which is located in the asteroid belt, the other dwarf planets are found in the outer solar system. There are another 6 objects in our solar system that are almost certainly dwarf planets and there may as many as 10,000. 

Pluto

Eris

Haumea

Makemake

Ceres

        Currently none of the dwarf planets have been visited by space probes, though in 2015 NASA’s Dawn and New Horizons missions will reach Ceres and Pluto respectively.

What Is Dwarf Planet?
Dwarf planets share many of the same characteristics as planets thought there is one significant difference. The International Astronomical Union’s definition of a dwarf planet is:

A “dwarf planet” is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
(c) has not cleared the neighbourhood around its orbit, and
(d) is not a satellite.

The key difference is that a planet has cleared other objects in the area of its orbit while a dwarf planet has not.

Sizes Of The Dwarf Planets
The largest dwarf planet in the solar system could be either Eris or Pluto followed by Makemake and Haumea with the smallest being Ceres. The order of the dwarf planets from closest to Sun outwards is Ceres, Pluto, Haumea and Makemake with Eris being the furthest from the Sun.