This “gallows” was 8’ tall. In order to be double the height of the man standing on it, the man standing on it had to be a midget.
The gallows includes the scaffold. It's referred to as a "New Drop" gallows, first used in 1760 in England.
Such gallows are either "short drop" or the later "long drop".
In the picture, for accuracy, it appears to be about 12 feet tall.