Adult body sizes of both sexes vary from 3.5 to 6.0 cm (1.4–2.4 in) (apex of elytra to apex of thoracic horn), with captive-reared individuals reaching up to 8.0 cm (3.1 in)[2] Coloration of the elytra varies from white to grayish-white, often with irregular black spots of various size and number.

Like other Hercules beetle species, Dynastes grantii undergoes a six-stage life cycle from egg to adult, with three larval instars and a single pupal stage.

[1][2] This species typically inhabits highland forest habitats, at or above 1,600 m (5,200 ft) above sea level.

The beetles strip the bark from small branches and feed on the sap produced by the exposed cambium.

The significant protrusion forward of the bottom tooth at the base of the thoracic horn in males of Dynastes hyllus is also a distinguishing factor between the two species.