Each character on the page takes up quite a bit more space, too. I imagine you have to go to newspaper folio sizes if you want to keep the same number of pages.
The wikipedia page for Braille Transcription says:
Braille characters are much larger than their printed equivalents, and the standard 11" by 11.5" (28 cm × 30 cm) page has room for only 25 lines of 43 characters.
However, it also goes on to say that braille is usually written in an abbreviated or “compressed” form where single braille characters stand in for common words, like “b” for “but” or “c” for “can”. If the standard printed page has 66 lines and ~80 characters per line, that’s about 5KB of textual information per page. Without the previously mentioned compression, Braille can only get about 1KB per page.
So, a book in Braille would most likely have somewhat more pages than the same book printed using more traditional means, in addition to using much heavier paper for each page, and much larger pages.