Surface pressure, in the context of planets, refers to the atmospheric pressure exerted at the planet's surface. It represents the force per unit area exerted by the planet's atmosphere on a surface located at the planet's boundary.

The surface pressure of a planet is primarily determined by the mass of its atmosphere and the gravitational force acting on it. It is a measure of the weight of the overlying atmospheric column per unit area.

On Earth, the standard atmospheric pressure at sea level is approximately 101.3 kilopascals (kPa), or 1 atmosphere (atm). This means that the weight of the Earth's atmosphere exerts a pressure of 101.3 kPa on a surface area of 1 square meter at sea level.

Surface pressures can vary significantly among different planets. For example, Venus has an extremely dense atmosphere, resulting in a surface pressure of about 92 times that of Earth, or roughly 9.2 megapascals (MPa). This high surface pressure on Venus is due to the massive amounts of carbon dioxide present in its atmosphere.

Other planets, such as Mars, have much lower surface pressures. Mars has a thin atmosphere composed mainly of carbon dioxide, resulting in a surface pressure of around 0.6% that of Earth, or about 0.006 atm.