An optical sight configured to be mounted to a weapon includes a lens assembly, a display, and a controller. The display is configured to display a target animal through the lens assembly. The controller is configured to determine a range from the optical sight to the target animal and display the range on the display. The controller is configured to determine an animal type, a known animal dimension, and a display area for the target animal, where the display area for the target animal is a percentage of the display occupied by the target image. The controller is configured to determine the range from the known animal dimension and the display area for the animal.