What is the length of day for Mercury in Earth days?

Answer 1

To understand the length of a day on Mercury, it is important to know the length of a Mercurian year. (Actually you don't need to know that.)

Mercury orbits the sun in about 88 Earth days. It rotates on its axis (day) three times for every two orbits around the Sun (year). A Mercurian year lasts about one and a half Mercurian days. That's about 58.65 Earth days for the length of

a day on Mercury.

Remember though that this is called a "sidereal day". There's also another day

called the "solar day". This is based on the apparent journey of the Sun round

the sky. For Earth these two days are only slightly different, but for Mercury the

difference is huge. The solar day is about 176 Earth days on Mercury.

Answer 2

One year on Mercury is about 88 Earth days long, 3/4 of a Mercurian day.