How much is a Revius?
The original Halachic measurement in dimensions of a cup: The measurement of a Revius by completely square cup is two fingers [i.e. Etzbaos] in width and length and 2.7 fingers in height. The measurement of a Revius by a round cup is two fingers in width and length and 3.6 fingers in height.
The practical measurement in volume CC: Practically, there is a dispute amongst the Poskim regarding the length of this “finger” measurement, which consequently created a dispute regarding the exact amount in fluid measurements that a Revius contains: Some Poskim rule that a Revius is equivalent to 86.4 milliliters or 2.92 fluid ounces. This measurement is the same Gematria as the word כוס. This opinion is known as Shiur Rav Chaim Neah. Other Poskim rule it is equivalent to 81 milliliters or 2.73 fluid ounces. Other Poskim rule it is equivalent to 84 milliliters or 2.84 fluid ounces. Other Poskim rule that it is equivalent to 99 milliliters or 3.34 fluid ounces. Other Poskim rule that it is equivalent to 108.8 milliliters or 3.67 fluid ounces. Other Poskim rule that it is equivalent to 115.2 milliliters or 3.89 fluid ounces. Other Poskim rule that it is equivalent to 118 milliliters or 3.99 fluid ounces. Other Poskim rule that it is equivalent to 120 milliliters or 4.05 fluid ounces. Other Poskim rule that it is equivalent to 123 milliliters or 4.16 fluid ounces. Other Poskim rule that it is equivalent to 150 milliliters or 5.07 fluid ounces [Gematria of כוס הגון]. This is known as Shiur Chazon Ish. Other Poskim rule that it is equivalent to 168 milliliters or 5.68 fluid ounces. Practically, the widespread custom of the world, Sephardim, Chassidim, and Ashkenazim, follows the first opinion above, for the cup to suffice to contain a minimum of 86 milliliters which is the same Gematria as the word Kos. This applies whether Lechumra or Lekula [to be stringent or lenient], including even for Safek Brachos. However, there are some members of Lithuanian Jewry who are initially stringent like the Shiur Chazon Ish of 150 milliliters. Likewise, some in Chabad are initially stringent like some of the other opinions mentioned.]
Areas in Halacha that a Revius is relevant:
In Halacha, the measurement of a Revius is relevant for various Halachos including:
- After blessing: One must consume a Revius of liquid [within a certain amount of time] in order to be able to say an after blessing.
- The size Kiddush cup to buy or use for Kiddush, Havdalah, Four cups of Pesach, Kos Shel Bracha: One must use a cup that holds a Revius of wine or other valid beverage in order to be Yotzei Kiddush, Havdalah, or other Kos Shel Bracha.
- The amount to drink by the four cups on Pesach: Although during Kiddush of Shabbos and all Yomim Tovim one is not required to drink majority of the Kiddush cup so long as he drinks the measurement of Malei Lugmav, nevertheless, by the four cups of the night of the Seder one is to initially drink the entire cup of wine.
- Kiddush Bemakom Seuda: One who drinks a Revius of wine after saying Kiddush is considered to have fulfilled Kiddush Bimakom Seuda.
- Simcha on Yom Tov: Some say that men must drink at least a Revius of wine on Yom Tov and Chol Hamoed in order to be Yotzei the Mitzvah of Simcha.
- Tasting food: One who tastes a Revius of a drink is to say a before blessing even if plans on spitting it out.
- The morning Netilas Yadayim: The vessel used to pour the water must contain at least a Revius worth of water prior to beginning the first pouring. [If it does not contain a Revius worth of water, the washing is invalid.] [If one spills a Revius of clean water into the impure water of the morning washing, one may learn Torah in its presence.]
- Netilas Yadayim for bread: The vessel used to pour the water must contain at least a Revius worth of water prior to beginning the first pouring, otherwise the washing is invalid.
- Nullifying urine: If one pours a Revius of water into urine, the urine is considered nullified and one may learn Torah and Daven near it.
- Davening after drinking wine: One who drinks a Revius of wine or alcohol, has certain limitations regarding Davening.
- Avoda Bamikdash and Nesias Kapayim: One who drinks a Revius of wine or alcohol, may not serve in the Temple. Likewise, a Kohen may not perform Nesias Kapayim if he drank a Revius of wine.
- Zimun: One who drinks a Revius of liquid can join others for a Zimun.
The accustomed ruling is that a Revius is 86 milliliters for all Halachic matters whether for stringency or leniency, although some are stringent for it to contain 100, or 115, or 150 milliliters.
 Admur 472:18; Tur 472; Levush 472:9; Rav Chisda Pesachim 109a; Kaf Hachaim 472:57; See the following Poskim that the measurement of a Revius is equivalent to the volume of one and a half eggs with their shell. [Admur Seder 8:1; Luach 2:1; M”A 210:2 and 5; Taz 210:1; Bach 210; Rosh 14:5; Rif; Drashos Maharil Hilchos Agada; Chok Yaakov 472:11; Elya Raba 210:8; 472:13; Chok Yosef 472:10; P”M 472 A”A11; Kaf Hachaim 472:57]
Other opinions: See Rebbe Yosa in Yerushalmi Pesachim 10:1 that the measurement is 2×2 fingers by 1.88 Etzba height
 Some Poskim rule that the finger is 6 barley kernels worth [Admur after the retraction, as recorded in Sheiris Yehuda Y.D. 11 and Tzemach Tzedek 102 and 320] which is equivalent to 2 centimeters in length. [See list of Poskim, Geonim, Rishonim and Achronim in Shiureiy Torah 1:1 footnote 8 page 75; 3:25 footnote 58 page 249 and also page 16; Tikunei Mikvah p. 89 and 93 that the Shiur of Admur after the retraction is 2.16 cm; See Shiureiy Mikvah p. 83 who negates this opinion; The tradition of the Rebbe Rashab is that it is 2.22 cm; Another tradition is that it is 2.3 cm] Thus, a square cup is 4×4 with a height of 5.4 centimeters, while a round cup is 4×4 with a height of 7.6 centimeters. [Shiureiy Torah ibid page 75] Other Poskim rule that the finger is seven barley kernels worth [Admur 190:13; See Poskim in Shiureiy Torah ibid] worth which is equivalent to 2.5 cm. [See Tikunei Mikvah p. 88 and 93] Thus, a square cup is 5×5 with a height of 6.75 centimeters, while a round cup is 5×5 with a height of 9 centimeters.
 See Shiureiy Torah 3:6 and in chapter 1 in length; Koveitz Yagdil Torah NY 60 p. 263-264 in a Ksav Yad of Tzemach Tzedek in name of Admur; Kitzur Hilchos Shabbos Miluim p. 18; Tikkunei Mikvaos [Levin] chapter 10 p. 93
The ruling of Admur: There is a difference in ruling recorded between what Admur ruled in his Shulchan Aruch regarding the measurement of an Etzba versus what he ruled later on in his advanced age, as recorded in Sheris Yehuda Y.D. 11 and Tzemach Tzedek 102 and 320. In the Shulchan Aruch Nida 190:13 he ruled that the Etzba is 7 barley kernels worth, while in his advanced age he ruled that it is 6 barley kernels worth. [See Shiureiy Torah ibid; Tikkunei Mikvaos ibid] Now, while all agree that the measurement of the retraction is smaller than that of Admur’s original ruling in his Shulchan Aruch, there exists various opinions and traditions in Chabad as to its exact centimeter measurement and consequential fluid measurement even if we follow his retraction. One tradition has it that Admur stated that the Satka of Nikolaiy is the measurement of a Revius. [Shiureiy Mikveh p. 83] Rav Avraham Chaim Naah in Shiur Torah insists that the measurement remains of the finger remains as 2 centimeters. Other traditions are recorded from the Tzemach Tzedek, Rebbe Rashba and Rebbe Rayatz, as will be explained. Practically, the Shiur Revius according to Chabad tradition and understanding of Admur varies between: 86.6 milliliters, 99 milliliters, 108.8 milliliters, 115.2 milliliters, 118 milliliters, 120 milliliters, to 123 milliliters.
 Rav Avraham Chaim Naa”h in Shiureiy Torah 3:6 based on retracted ruling of Admur in Sheiris Yehuda Y.D. 11 and ruling of Rambam that a Revius contains 27 Draham; This follows the Grach Na’ahs opinion in the Shiur Kibeitza which is 57.7 grams, and thus a Revius equals 86.6 milliliters which is equivalent to 1.5 eggs with their peel, as rule the Poskim ibid in previous footnotes; Maharsham 9:8
 Rav Mazuz; Rav Ovadia Yosef; See Shiureiy Torah 3 footnote 58 [page 250] that this possibility is mentioned
 Ruling of Geonim, brought in Shiureiy Torah ibid
 Tradition of Rav Eliyahu Landa Shlita, based on tradition from Admur that the Satka of Nikolaiy is the measurement of a Revius, and that the Satka contains 99 milliliters. Shiureiy Mikveh p. 83 that the Kiddush cup of the Rebbe Raytaz contained 100 milliliters
 Tikkunei Mikvaos p. 93 based on calculation of retracted ruling of Admur in Sheiris Yehuda Y.D. 11 that each Etzba is 2.16 cm
 Tradition from Tzemach Tzedek in name of Admur, brought in Shut Tzemach Tzedek O.C. 84; See Tikkunei Mikvaos ibid
 Tikkunei Mikvaos p. 93 based on ruling of Rebbe Rashab that the Etzba is 2.22 cm
 Shiureiy Mikveh p. 83 based on tradition from Admur that the Satka of Nikolaiy is the measurement of a Revius, and some say the Satka contains 120 milliliters.
 Tikunei Mikvaos p. 94 based on tradition from Admur that the Satka of Nikolaiy is the measurement of a Revius, and some say the Satka contains 123 milliliters.
 Chazon Ish in Kuntrus Hashiurim and in letter to Gr”ach Naah that so was custom in Lita, and is based on all the following Poskim who rule Niskatnu Habeitzim: Opinion brought in M”B 271:68; 486:1 and Biur Halacha 271:13 “Shel Revius”; 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;
 Tikkunei Mikvaos p. 93 based on Admur in Y.D. 190:13 [prior to his retraction] that the Etzba is 7 barley kernels worth
 See Visein Barcha p. 248 and Piskeiy Teshuvos 201:1 that so was the widespread custom of the world to follow 86 milliliters as the Shiur Revius, as evident from the Kiddush cups of many Gedolei Yisrael, including the Chofetz Chaim; Yechaveh Das 4:25 that so was the widespread custom in all Sephardi communities; Rav SZ”A in Halichos Shlomo 2:90 “The main opinion is like the Grach Naah, and so is the old age custom”; Rav Elyashiv Koveitz Teshuvos 2:30 “I have already publicized my opinion that the accepted Shiur is like the Grach Naah”; Shevet Halevi 6:60 that from the Setimas Haposkim it is implied unlike the Tzelach
 As rules M”B ibid and ibid regarding Lechtachila for Biblically rooted Mitzvos; See Piskeiy Teshuvos ibid that although today many people have taken upon themselves the 150 milliliters Shiur of the Chazon Ish, nevertheless, Bedieved if one only drank 86 milliliters a n after blessing is to be said.
Ruling of Mishneh Berurah: See M”B 271:68; 486:1 and Biur Halacha 271:13 “Shel Revius” where he arbitrates to initially suspect for this opinion by all possible Biblical Mitzvos [i.e. Kiddush of Shabbos night, Havdala, however not for blessings and Rabbinical Mitzvos]. To note, however, that his own Kiddush cup was not this Shiur!
 Admur in Seder 8:1; Luach 2:1; Michaber 210:1; Rambam Brachos 3:12
 See Admur in Seder 8:6; Luach 2:7; 472:20; 612:15; Shiureiy Torah 3:15; Practically, the Revius must be consumed within 3-4 minutes to say an after blessing.
 See regarding Kiddush: Admur 271:20; 28; M”A 271:23; See regarding Havdalah: Admur 296:13See regarding four cups on Pesach: Admur 472:17; Michaber 472:9; Pesachim 108b and Rashbam ibid, Ran ibid; Beis Yosef 472; Bach 472; M”B 472:62; Kaf Hachaim 472:62
 Admur 472:19; See Piskeiy Teshuvos 472:8
 Admur 271:24; 472:19; See also 190:4; Michaber 271:13; Rav Huna Pesachim 107a; Ketzos Hashulchan 79:5
 Admur 273:9; 274:8; 286:4; Rama 273:5
 Nimukeiy Orach Chaim 529; Torah Or Esther p. 198 “One fulfills his obligation of Simcha through drinking a Revius of wine.”
 Admur Seder 8:11 “Even if he tastes a lot, up until a Revius, not including a Revius” and Luach 8:12 “Even if he tastes a lot, up until a Revius”; Ohel Moed Shaar Brachos 1:4 brought in Beis Yosef 210; Interpretation of Braisa Brachos 14a “Tasting does not need a blessing, up until a Revius”; Semag, brought in Erech Hashulchan 210:7 and Kaf Hachaim 210:30; This possibly follows the 1st opinion in Michaber ibid and Tur 210 in his Stam/main opinion and the Rif and Rambam Brachos 1, as they can be interpreted to be referring even to spitting out a Revius that a blessing is required, and so learns Ateres Zekeinim 210, however see Beis Yosef 210 brought in other opinions
Other opinions: Some Poskim rule a blessing is never recited upon tasting a food without swallowing it, even if it is more than a Revius of food. [2nd opinion in Michaber ibid; Tosafus in name of Rabbeinu Chananel; M”A 211:7 and 10 that this is the main opinion; Rama ibid concludes that Safek Brachos Lihakel. This means that a blessing is not to be recited upon tasting a food unless one a) swallow the food as requires second opinion and b) eats a Revius as requires the first opinion. [Ateres Zekeinim 210 in explanation of Rama ibid] Some Poskim rule that even according to the 1st opinion in Michaber ibid and Tur 210 in his Stam/main opinion and the Rif and Rambam Brachos 1 a blessing is never said unless one swallows, even if he tastes a Revius, and they only argue if one swallows less than a Revius. [Beis Yosef 210 in argument against Ohel Moed ibid; M”B 210:15]
 Siddur Seder Netilah; Kama 4:1; 159:3; 160:16; and Seder Netila 12 regarding washing for bread.
 Based on Siddur Seder Netilah; Biur Hagra 4:7 in name of Rieh; Rashash in Nehar Shalom; Ruach Chaim 5:5; Kaf Hachaim 4:26
Background of ruling of Siddur: Admur writes in the Siddur that all the laws of washing for a meal equally apply for the morning washing. In 159:3 and 160:16 Admur rules regarding washing for bread that the vessel must contain a Revius of water for it to be valid and hence the same would apply for the morning washing.
Other opinions-Ruling of Kama: In Kama 4:3 Admur rules: “If one does not have a Revius of water available he may nevertheless wash with a blessing being that the Sages did not differentiate [in the amount of water], as one is nevertheless washing with valid water.” This follows the ruling of Michaber 4:6
 Ruach Chaim 77 brought in Kaf Hachaim 4:33; Toras Yekusiel 2; Beir Moshe 8:39 mentions nullifying in majority
If two people washed: If two people washed hands, then one requires two Revius of water to nullify it. [Kaf Hachaim ibid]
Other Opinions: Toras Yekusiel ibid brings Rabbanim who rule that even adding water does not help.
 Admur159:3; 160:16; and Seder Netila 12
 Admur 76:1; Michaber 76:1
 See Admur 99:1-3
 See Admur 128:51
 Admur 197:3 and 198:2