144. The Number of Verses per Aliyah

23:19 Each aliyah must consist of at least three verses. On Mondays, Thursdays and Shabbos afternoons, we need to read a total of at least ten verses, the third aliyah containing four verses. After the fact, if only nine verses were read, three for each oleh, the obligation has been fulfilled. (Though we should then read another three verses without saying the blessings – Mishnah Brurah 137:14.) On Purim, we only read nine verses, three per oleh, and that's okay because the entire topic being read from the Torah is only nine verses long.

23:20 The one reading from the Torah should not stop at a place where there aren't three verses from there to the next "open" or "closed" section. If the oleh has already said the bracha after the reading and there are fewer than three verses to the start of the next section, the baal korei need not go back and repeat verses. He can start where he left off but he must make sure to read at least three verses from the new section. If a section contains just two verses, one may stop between them. If there is a break in the middle of a verse, as occurs at the beginning of parshas Pinchas (Numbers 26:1), one may stop even at the preceding verse.