The acceleration due to Earth's gravity (see standard gravity) at its surface is 976 to 983 Gal, the variation being due mainly to differences in latitude and elevation. Mountains and masses of lesser density within the Earth's crust typically cause variations in gravitational acceleration of tens to hundreds of milligals (mGal). The gravity gradient (variation with height) above Earth's surface is about 3.1 µGal per centimeter of height (), resulting in a maximal difference of about 2 Gal (0.02 m/s2) from the top of Mount Everest to sea level.