The snow line is the point above which, or poleward of which, snow and ice cover the ground throughout the year.

The interplay of altitude and latitude affect the precise placement of the snow line at a particular location. At or near the equator, it is typically situated at approximately 4,500 meters (or about 15,000 feet) above sea level; this parameter becomes progressively lower as the latitude increases, falling all the way to sea level itself near the poles.

In addition, the relative location of a mountain to the nearest coastline can be a factor in how high the snow line would be; a peak near a coast — especially the west coast — of a continent might have a lower snow line than one of the same height and at the same latitude situated in a landmass interior, because the average summer temperature of the surrounding lowlands would be warmer in the latter spot than in the former, thus making a higher altitude necessary to keep the snow from melting in the summer.

See also tree line.