Which planet is closest in size to Earth?

Venus is the planet closest in size to Earth. Its diameter is about 12,104 kilometers, compared with Earth’s average diameter of about 12,742 kilometers, making Venus roughly 95% as wide. Its mass is about 81.5% of Earth’s, and its volume is about 85.7%. These similarities are why Venus is often called Earth’s “sister planet” or “twin.”

The resemblance is mainly structural: both are rocky terrestrial planets with iron cores, rocky mantles, and solid crusts. Venus also formed in the inner Solar System, relatively near Earth’s orbit. However, similar size does not mean similar conditions. Venus has a dense carbon-dioxide atmosphere, sulfuric-acid clouds, surface pressure about 93 times Earth’s, and temperatures around 464°C.

A common mix-up is Mercury, the smallest planet. Mercury is much smaller—about 38% of Earth’s diameter—while Mars is about half Earth’s diameter. Venus is also closer to Earth than any other planet at its nearest approach, although that fact is separate from its size comparison.