Wearing a Tallis Gadol properly-Making sure to cover at least one Ama of the body:[1]

The Tallis Gadol must be worn in a way that it covers one’s actual body. Those who cover with their Tallis only their head and around their neck, and are not particular to cover their body, are to be protested.^[2] [One who says a blessing on such a wearing is saying a blessing in vain.[3] Likewise, those who wear the Tallis in a way that it is folded and draped over ones shoulders, with the strings of the two right corners resting on ones right chest, and the two left corner strings resting on one’s left chest, do not fulfill the Mitzvah and are to be protested.[4]]

How much of the body must the Tallis cover:[5] The Tallis Katan and Gadol[6] must be worn in a way that the width of at least one Ama [49 cm] of material, and the total length of at least two Amos [98 cm] is spread open and covers the person’s body.[7] The folded areas of the Tallis are not included in the above size. [Thus, those who role the sides of the Tallis Gadol in a way that the Tallis does not cover 49 cm of the width of the back body, or 98 cm of the length of the body, are mistaken and do not fulfill the Mitzvah.[8]]

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[1] Admur 8:8; M”A 8:2; Beis Oved 27; Shalmei Tzibbur p. 32; Kaf Hachaim 8:9

^[2] The reason: As according to all opinions, the main “wearing” of a Tallis is when one is wearing the Tallis over one’s body. The argument brought in 8:5 is only regarding if the Tallis must also be placed over one’s head, however covering the head alone without covering the body, according to all does not suffice to be considered clothing at all. [Admur ibid; See 10:20 regarding a scarf, that for this reason it is exempt from Tzitzis.]

[3] See Shaareiy Teshuvah 8:3

[4] M”A 8:2; Masas Binyamin 48; Poskim in Kaf Hachaim 8:9; See Nehar Mitzrayim 1 which says that most Egyptian Jews wear the Tallis this way and they are to be taught to wear it properly, at least for the time of the blessing.

[5] Siddur Admur [4 and 11 in Raskin] “This entire measurement of the width and length of the Tallis Katan needs to be entirely spread open, and clothe the person throughout its entire measurement, as the verse states “Asher Tichaseh Bah”. This teaches us that the above required measurement must cover the person and may not be folded or dented in any amount, being that the folded and bent area is not included in the measurement.”

Other opinions: Some Poskim rule that the folded areas are included within the Shiur of the Tallis, being that the folded area is meant to be spread open, and hence it is not necessary to prevent the Tallis Katan from folding. [Beis Yaakov 106; Beir Heiytiv 16:1; Bnei Chayi 16; M”B 16:4; See also Michaber 10:6; Admur 10:13; Tehila Ledavid 16:2] The world is not accustomed like this opinion of Admur in his Siddur. [Piskeiy Teshuvos 16:3]

[6] This Halacha in Admur in the Siddur is stated regarding the Tallis Katan, although he repeats the same concept also regarding the Tallis Gadol in letter 12 [in Siddur Raskin] “However one must beware that also during the Atifa the Tallis Gadol covers his front the width of an Ama that is spread open.”

[7] Must the Ama in width and length cover the body both in front and back? Admur ibid [Siddur 4] does not explicitly mention whether the Shiur Tallis must cover both the front and back or if it suffices to have it all in the back. By a Tallis Katan there is no other choice, and hence both the front and back must be covered one Ama in both length and width, as only then is one’s body covered for two Amos. However, by a Tallis Gadol, perhaps it suffices to have two Amos cover from one’s shoulders until the back. Perhaps it is due to this that when we wear the Tallis during Davening we are not particular that the front be covered by an Ama, and hence allow to fold the Tallis on the shoulders. However, in letter 12 [in Siddur Raskin] of the Siddur Admur states “However one must beware that also during the Atifa the Tallis Gadol covers his front the width of an Ama that is spread open.” Likewise, in Siddur letter 11 [in Siddur Raskin] Admur writes that even according to Nigleh “it is proper that the main Atifa not be only in the back but also in the front until below the chest in order so one be surrounded by Mitzvos” Vetzaruch Iyun Gadol why we are not accustomed to cover an Ama in the front of the body, despite Admur explicitly requiring also the front to be covered an Ama, as explained from the Siddur

How much of the back should the Tallis cover? Some Poskim write that one is not to have the Tallis drag all the way down the back but is rather to cover until slightly below the waist [for at least one Ama]. The reason for this is because until the chest is the aspect of the Tallis while from there and onwards is the aspect of the Tzitzis. [Asara Mamaros; Shaareiy teshuvah 21:5; Kaf Hachaim 21:18]

[8] Pashut; Heard from Rav Eliyahu Landa