Estimate time to read a book series.
Page counts are not comparable across editions, so the reliable route to reading time is words. A typical trade paperback page carries around 275 words, which turns pages into a word count, and dividing by your words-per-minute rate gives reading minutes. Spreading those minutes over your daily habit gives a realistic calendar for a long series rather than an optimistic per-book guess.
Series word count
Total words = books x average pages per book x 275 words per page
Calendar time
Reading minutes = total words / words per minute; days = reading minutes / minutes read per day
Adult silent reading averages around 200 to 300 words per minute for fiction. Dense non-fiction or unfamiliar terminology can drop it below 150.
Font size, trim size and leading vary hugely between editions, so a 400-page hardback and a 400-page mass-market paperback can differ by more than fifty percent in actual text.