It takes Mercury 88 Earth days to circle the Sun once. This period is Mercury's orbital period, or the length of one Mercury year.
Mercury has the shortest year of any planet because it is the closest planet to the Sun. Its average distance from the Sun is about 58 million kilometers, or 36 million miles. Mercury also travels faster than any other planet, moving through its orbit at roughly 47 kilometers per second.
The number 88 is often confused with Mercury's day. Mercury rotates once on its axis in about 59 Earth days. Because its rotation and orbit interact in a 3:2 spin-orbit resonance, a complete solar day on Mercury—from one sunrise to the next—lasts about 176 Earth days. In other words, a day-night cycle takes twice as long as a Mercury year.
Mercury's proximity to the Sun does not make it the hottest planet overall. Venus is hotter because its thick carbon-dioxide atmosphere traps heat far more effectively. Mercury instead has extreme temperature differences between its sunlit and dark sides.