Convert from ridge to palm [US, Roman major]

Unit Definition (ridge)
The ridge is a traditional Welsh unit of distance equal to 3 leaps or 20 feet 3 inches (6.1722 meters).

Unit Definition (palm [US, Roman major])
A palm, when used as a unit of length, is usually four digits or three inches, i.e. 7.62 cm (for the international inch). The width of an adult human male palm is indeed about 10 centimetres.In English this unit has mostly fallen out of use, as do others based on the human arm: digit (¼ palm), finger (7/24 palm), hand (4/3 palms), shaftment (2 palms), span (3 palms), cubit (6 palms) and ell (15 palms).