Reference of Measurements in Halacha

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Kezayit

  1. According to Ashkenazim, all sizes are measured in volume and not weight. [1]However, according to Sephardim the actual halacha is that measures are in volume but the minhag is to follow the measures in weight. [2]
  2. There’s a dispute in the rishonim whether the kezayit (olive size) is a half or third of a KeBeytzah (egg size), and the halacha follows the opinion that a Kezayit is half a KeBeytzah. [3]
  3. According to Rav Chaim Noeh, the Kezayit for Deoritta measures (eating Matzah) and Bracha Achrona is 25.6 cc (in volume). Nonetheless because food stuck in between one's teeth doesn't count towards a Kezayit eaten one should make sure to have 28.8 cc. Regarding a Kezayit for derabbanan measures (eating maror) the kezayit is 17.3 cc. [4] The Chazon Ish’s opinion is that the Kezayit is 33.3 grams (1.3 oz). [5]
  4. The minhag of the world and many other authorities is to follow Rav Chaim Noeh’s opinion. [6]

KeBaytzah

  1. According to Rav Chaim Noeh, the KeBaytzah is 55cc and according to the Chazon Ish is 100cc. [7]

Kedi Achilat Pras

  1. According to Rav Chaim Noeh, the Kedi Achilat Pras is 4 minutes for measuring eatings for a mitzvah or bracha Achrona, however regarding a sick person eating in intervals on Yom Kippur the Kedi Achilat Pras should be measured as 9 minutes. [8]

Amah, Tefach, Etzbah

  1. According to Rav Moshe Feinstein, the Amah is 21.25 inches (53.98 centimeters), the Tefach is 3.54 inches (9.00 centimeters), and the Etzbah is 0.89 inches (2.25 centimeters). [9]
  2. According to Rav Chaim Noeh, the Amah is 18.90 inches (48 centimeters), the Tefach is 3.15 inches (8 centimeters), and the Etzbah is 0.79 inches (2 centimeters) [10]
  3. According to the Chazon Ish, the Amah is 24 inches (60.96 centimeters), the Tefach is 4 inches (10.16 centimeters), and the Etzbah is 1 inch (2.54 centimeters). [11]

How large is a Reviyit?

  1. A Reviyit is a Kebaytzah and a half. [12] Therefore, according to Rav Chaim Noeh, the Reviyit is 86 grams (3 oz) and according to the Chazon Ish the Reviyit is 150 grams (5.3 oz). [13]

Practical applications

  1. If one ate between a third and a half a KeBaytzah one should not make a Bracha achrona because of safek Brachot. Therefore, one should have less than a third and not make a Bracha achrona or more than a half and make a Bracha achrona. [14]
  2. On מצות Deoritta such as eating Matzah one must be strict to hold a Kezayit is a half a Kebaytzah. However, regarding מצות Derabbanan it’s preferable to hold that a kezayit is a half a kebaytzah, however, one may rely on the opinion that a kezayit is a third a kebaytzah. [15]

References

  1. Mishna Brurah 456:3, Vezot HaBracha (pg 6)
  2. Yalkut Yosef (Klalei Brachot pg 195-202) discusses this at length
  3. S”A 486 rules like Tosfot and not the Rambam that the Kezayit is half a Kebaytzah and not a third.
  4. Shiurei Torah (by Rav Chaim Noeh, Siman 3 Seif 13 pg 191)
  5. Vezot HaBracha (pg 6)
  6. Vezot HaBracha (pg 6, Birur 1, pg 221) in name of Rav Elyashiv and Rav Shlomo Zalman that one may follow Rav Chaim Noeh’s opinion and there’s no need to be strict for the Chazon Ish’s opinion. Vezot HaBracha also mentions that such is the minhag of the world.
  7. Vezot HaBracha pg 6
  8. Shiurei Torah (by Rav Chaim Noeh, Siman 3 Seif 15 pg 203)
  9. Sh”t Igrot Moshe O”C 1:136. writes that the Amah is 21.25 inches and one can be strict to hold that it is 23 inches.
  10. Shiurei Torah (by Rav Chaim Noeh, Siman 3 Seif 25 pg 249)
  11. Shiurin shel Torah (pg 3) by the Steipler quoting the Chazon Ish but admitting that these are approximate measures because of the need to publicize the measures but not an accurate calculation.
  12. Mishna Brurah 486:1
  13. Vezot HaBracha (pg 6)
  14. Mishna Brurah 486:1
  15. Mishna Brurah 486:1