An adult alpine marmot is between in head-and-body length and the tail measures from . The body mass ranges from , with the animals being significantly lighter in the spring (just after hibernation) than in the autumn (just before hibernation). The alpine marmot is sometimes considered the heaviest squirrel species, although some other marmot species have a similar weight range, making it unclear exactly which is the largest. Its coat is a mixture of blonde, reddish and dark gray fur. While most of the alpine marmot's fingers have claws, its thumbs have nails.