Further or Farther?

"You’re navigating to a new coffee shop—but is it one mile further or farther down the road? With a difference of only one letter, it can be hard to remember when to use "further" vs. "farther," especially because both words generally mean “more distant.” For a time, speakers and writers did not differentiate between the two terms. However, a recent rule has established a clear separation between them. "Farther” refers to physical distance, while “further” refers to metaphorical distance, extension of time, or degree. "Further" can also mean "in addition to.""

— Kim Bussing (www.thoughtco.com)