The Brothers Karamazov runs to about 920 pages in a common edition, divided into four parts, twelve books and an epilogue, with 96 numbered chapters plus the preface "From the author." The number varies with format and font size, but it is one of the author's longest novels.
The books vary greatly in size. Book VI, with Zosima's life, has only three chapters; Book XII, the trial, has fourteen. The chapters vary too: there are those of a single scene and those that gather a whole day of visits and conversations.
For reading at an unhurried pace, the reading schedule divides the book into 12 weeks, about 11 pages a day, with breaks at chapter ends. In practice, some weeks are lighter and others heavier, because the chapters are not all the same length: the first week covers the preface, the family's history and the beginning of the meeting in the cell, and the last ones cover the end of the trial and Ilyusha's funeral.
The novel was serialized in The Russian Messenger, from 1879 to 1880. If you read on an e-book or a phone, the page count changes, but the count of parts, books and chapters does not: they are the best measure for planning your reading.