About 10% of Earth's land surface is covered by glaciers. This total includes enormous ice sheets in Antarctica and Greenland as well as smaller mountain glaciers in ranges such as the Himalayas, Andes, Alps, and Rockies.
Glaciers are persistent masses of ice that form on land and move slowly under their own weight. Although they cover only about a tenth of Earth's land, roughly 99% of all glacial ice is concentrated in the polar ice sheets. Antarctica alone is almost entirely ice-covered, while Greenland holds the other major continental ice sheet.
The figure refers to land area, not the entire surface of Earth. Since oceans cover most of the planet, glaciers occupy a much smaller percentage of Earth's total surface area. Glaciers are also different from sea ice, which forms when ocean water freezes and does not originate as flowing land ice.
This coverage is not fixed. Glaciers expand when snowfall and other accumulation exceed melting, sublimation, and ice loss, and shrink when ablation is greater. Modern glacier retreat is reducing the area covered by many mountain glaciers.