Still extant are 591 (AT) + 142 (NT) = 733 old parchment folios. The lost pages were replaced by parchment folios written in minuscule script. All pages have been numbered throughout with Arabic numbers later (1 - 1536).
The AT runs from folio 1 to 632 = 1264 pages. 31 folios = 62 pages are missing at the beginning (Gen. 1 - 46:28. These have been replaced by 20 folios (= 40 pages) in minuscule script. Also 10 folios are missing from the Psalms (Ps 105:27 - 137:6). These have been replaced by 6 folios (= 12 pages) in minuscule script.
2. Sa 2:5-7 and 2:10-13 are lost by destruction (cut off). The Macc. books were never included in the codex.
The NT begins with folio 633 (Chi-Lambda-Gamma) = originally page 1265. This is today page 1235. It consists of the Gospels (Mt, Mk, Lk, Jo), Acts, the Catholic letters (Jak, 1.-2. Peter, 1.-3. John, Jude) and the Pauline letters (Ro, 1.-2. Co, Gal, Eph, Phil, Col, 1.-2. Thess, Hebrews). The uncial breaks off at Heb 9:14 KAQA[RIEI and the rest of Hebrews and the Apocalypse have been replaced by 18 pages in minuscule script.
The present uncial part of the NT is written on 284 pages.
If we take the Nestle-26 text as database and calculate the needed pages, we get 6 pages for the remaining Hebrews and 23 pages for the Revelation. The Pastorals would take 11 pages. Kenyon also assumes 40 pages to be missing. We cannot be sure though if those books were really included originally in the codex.
So in total the codex originally contained 632 (AT) + probably 162 (NT) = 794 folios = 1588 pages.