Venus is, by far, the closest match to the Earth in size. Venus has a measured diameter that is just about 95 percent that of the Earth and a planetary mass equal to 81.5 percent of the Earth's.
None of the other planets in the solar system are very Earthlike. After Venus, the next-closest planet to Earth in mass and size is Mars. Mars has only half the diameter of the Earth and just over 10 percent of the mass. Venus is also similar to Earth in that it has a substantial atmosphere, though the surface pressure of Venus' atmosphere is 92 times greater than Earth's.