What is the volume/weight of a Kebeitza:

There exists a major debate amongst the Poskim[1] in regards to the volume size of the Kebeitza, which in turn has created a consequential debate regarding the volume size of a Kezayis. Some Poskim[2] rule that the Kebeitza egg referred to by the Talmud was of a larger size than we have available today, and hence its volume is 100cc. This approach is formally known as Shiur Chazon Ish. Other Poskim[3], however, rule that no change has occurred within the egg sizes from the times of the Talmud, and hence the volume of an egg [without its peel[4]] equals 54cc. This approach is formally known as Shiur Avraham Chaim Naah. Practically, the widespread custom of world Jewry, Ashkenazim and Sephardim, is like the latter approach, and hence a Kebeitza is measured as 54cc.[5] This is equal to 54 grams of water, and hence for simplicity purposes, rather than measuring the volume of the food to make sure it contains 54cc one can simply weigh it to see that it contains 54 grams [unless the food weighs more than water in which case its Kebeitza weight would be more than 54 grams, while if it weighs less than water, then its Kebeitza weight would be less than 54 grams, as explained above]. Nonetheless, there are some Jews of Lithuanian Jewry who are stringent like the former approach and measure the Kebeitza as 100cc/grams. This especially applies by a Biblical Mitzvah.[6]

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[1] See M”B 486:1; Piskeiy Teshuvos 486:1

[2] Opinion brought in M”B 271:68; 486:1 and Biur Halacha 271:13 “Shel Revius” [M”B 486:1 concludes to be stringent by a Biblical Mitzvah] ; Nodah Beyehuda Tzelach Pesachim 116a; Chasam Sofer O.C. 97 and 127; Maaseh Rav 74 and 105; Rav Chaim Volozhin in Shaareiy Rachamim 165; Ashel Avraham Butchach 272; Aruch Hashulchan 168:13 that so is custom

[3] Shiureiy Torah 3:9 it is 53.8cc if the egg is measured without the peel and 3:7 that it is 57.6cc if the egg is measured with the peel; Kaf Hachaim 81:3; 168:46; 486:1; The following Poskim rule that the Kibeitza is 18 Dirham, and each Dirham is equal to between 2.7-3.2 grams, thus totaling approximately 55 grams: Rambam

Other opinions: Some Poskim rule that the Beitza is 44 grams with the peel and 33 grams without the peel. [Mahariv brought in Shiureiy Torah 1:21; 3 footnote 30]

[4] This follows the ruling of the Shiureiy Torah ibid and the Chazon Ish 39:17 that the egg is measured with its peel, however the M”B 486 rules that it is measured with its peel. [See Midos Vishiurei Torah 15:16]

[5] Kaf Hachaim 486:1 that so is custom

[6] M”B 486:1 concludes to be stringent by a Biblical Mitzvah