relative to Times New Roman
All widths are normalized based on cap height. For example, 20pt Times is compared to 18.5pt Arial due to Arial’s taller cap height.
Letter widths are calculated from the Latin alphabet.
Word frequency is based on the 100,000 most common English words in the Google Books corpus. The full list of words and frequencies is available in top100000.json.
Sentence width is simply the average word width combined with the space width.
Thanks to Matthew Butterick for inspiring a new copyfitting metric.