Valve's Source game engine uses the Hammer unit as its base unit of length. This unit refers to Source's official map creation software, Hammer. The exact definition varies from game to game, but a Hammer unit is usually defined as a sixteenth of a foot (16 Hammer units = 1 foot). This means that 1 Hammer unit is equal to exactly 19.05 millimetres or 0.75 inches (3/4").