In the Shulchan Aruch, Orach Chayim, Chapter 486, Section 1, it is explained that a "k'zayit" (an olive-sized portion) mentioned in all contexts is not small or large but rather medium-sized. This olive is called an "aguri," which contains an agur of oil within it. Some say its measurement is equivalent to half an egg (50 grams according to the Chazon Ish, 27 grams according to the Gra), while others say it is slightly less than a third of an egg (33 grams according to the Chazon Ish, 17.3 grams according to the Gra).

It further discusses the amount of food needed for the Eruv, stating that the amount for two meals of Eruv is 18 grogorot (a type of measurement), which is like six eggs. Therefore, the grogora is one-third of an egg, making the olive smaller than the grogora. According to the first opinion, 18 grogorot for two Eruv meals is more than half an egg.

The Chak Yakov requires a k'zayit equivalent to half an egg even for maror (bitter herbs) because the blessing is recited over eating maror, and eating a k'zayit implies a significant amount. If the amount is not as specified, there is a concern that the blessing may be in vain. The Mishnah Berurah also brings this ruling, mentioning that it is lenient for someone who is weak.