Ibn Ezra on Genesis 26:12/אבן עזרא על בראשית כ״ו:י״ב

1A HUNDREDFOLD. The word sha’ar means the same as the Rabbinic term shi’ur (estimate, reckon). The meaning of me’ah she’arim (a hundredfold) is that Isaac was blessed in that the earth produced one hundred times more than what he sowed was estimated to produce. The word she’arim comes from the same root as sha’ar in For as one that hath reckoned (sha’ar) within himself (Prov. 23:7).