Measuring on Shabbos or Yom Tov for the sake of a Mitzvah & Shiureiy Mitzvah:
Regarding Shabbos the Poskim rule that it is permitted to measure on Shabbos a Mitzvah measurement [i.e. Medida Shel Mitzvah]. However, regarding Yom Tov the Poskim rule that is that it is forbidden to measure on Yom Tov even for the sake of a Mitzvah. Furthermore, this allowance to measure for the sake of a mitzvah only applies when the Mitzvah is being done with the actual item that is being measured, however, it is forbidden to measure an item when the measurement itself involves no mitzvah and simply causes an external Mitzvah to be fulfilled. [Practically, in answer to the seeming contradiction, one may only measure on Shabbos and Yom Tov those matters that are recognizable to all that they are being done for the sake of a Mitzvah, however, if their measurement is not apparent that it is being done for the sake of a Mitzvah, then it may not be done on Shabbos if one could have done the measuring before Shabbos or Yom Tov. However, if one could not do the measuring before Shabbos or Yom Tov, then one may do so on Shabbos or Yom Tov if it is for the sake of a Mitzvah, even if it is not apparent that it is being done for a Mitzvah sake. Thus, one may not measure Shiurei Mitzvah of weight or volume on Shabbos, such as wine for Kiddush, and Kezayis Matzah and Maror, if he could have done so before Shabbos.]
Case examples that permitted for need of Mitzvah:
- Measuring a Mikveh: It is permitted to measure a Mikveh for the sake of verifying its validity. Such as to measure if it contains a volume of 40 Seah.
- Measuring if Tuma can enter room next door: It is permitted for one to measure a hole that is in the wall of a room that contains a corpse if the room next door contains Kohanim, to see if it contains a circumference of one Tefach. This is done in order to determine whether the impurity can leave from the room which contains the corpse into the room next door [as if it indeed contains a Tefach circumference, then the impurity travels from one room to the other and the priests must leave the room next door].
- Measuring one’s belt to heal illness: It is permitted [for those women who are knowledgeable and practice the following incantation] to measure the belt of one who has a headache for the sake of determining the measurement in order to recite the incantation as is customarily done by women, as this is considered a measurement of a mitzvah [for the sake of healing a person suffering from a headache.] There is also no intrinsic prohibition in reciting the incantation on Shabbos.
It is permitted to measure the following matters on Shabbos and Yom Tov if one could not do so beforehand:
1. The four Amos in front of a person praying Shemoneh Esrei to ascertain whether one is allowed to pass.
2. The 2000 Amos for Techum Shabbos.
3. Measuring a Tefach and Ama for the purpose of a mitzvah.
4. Measuring a Revius of wine for kiddush.
5. Measuring a Kezayis and Kebeitza for a Halachic purpose, such as a Mitzvah for or an after blessing.
6. Measuring for a sick person on Yom Kippur.
7. Measuring if a food contains 60 times an Issur that fell inside.
8. All measurements that are done for the sake of the public.
May one weigh an item with a nondigital scale for the sake of a mitzvah?
Some Poskim rule that it is permitted to even weigh an item on Shabbos or Yom Tov for the sake of a mitzvah. Other Poskim, however, rule that it is forbidden to weigh an item on Shabbos or Yom Tov even for the sake of a mitzvah.
If one’s Tzitzis tore, may he measure it on Shabbos to see if it still contains a valid length?
Yes. This applies even if one could have measured it before Shabbos, as it is a Medida Shel Mitzvah which is apparent to all.
 See Piskeiy Teshuvos 306:25
 Admur 306:18 “It is permitted to measure a measurement of a Mitzvah”; 308:88; 317:4; Michaber 306:7; Mishneh Shabbos 157a
 The reason: As measuring measurements of Torah does not appear like a mundane act. [Admur 306:18; M”A 306:16]
 Admur 456:9 “If one desires to kneed dough on Yom Tov, one must beware to measure the flour from before Yom Tov, as on Yom Tov itself it is forbidden to measure even for the sake of a Mitzvah”; 506:1 “It is forbidden to measure on Yom Tov due to Uvdin Dechol..even for the sake of a Mitzvah such as to measure the amount of flour in his dough to know if it contains Shiur Challah, nonetheless he should not measure it but rather take according to estimation, being that he could’ve measured it before Yom Tov.”; Michaber 506:1; Michaber and Rama 456:3; Beitza 29a-b; Kaf Hachaim 506:2; 486:3
Other opinions: Some Poskim rule it is permitted to measure on Shabbos and Yom Tov for the sake of a Mitzvah, such as to measure the Shiur for Matzos, Maror and the four cups. [Simple implication of Michaber 306:7 and Admur 306:18 and 308:88; Pesach Hadvir 1 p. 196, Vol. 3 306:15; Implication of M”A 308:78; Rav SZ”A in SSH”K 29 footnote 103; Piskeiy Teshuvos 306:25; 506:2; Or Letziyon 2:25-2; Yechaveh Daas 1:16] Nonetheless, even they agree that initially one is to measure before Y om Tov. [M”B 618:21 in name of Achronim; Piskeiy Teshuvos 306:25] Some Poskim limit the above allowance and rule that one may only measure in volume and not weight. [Kaf Hachaim 306:63; Kinyan Torah 5:22; See Piskeiy Teshuvos 306:25; 506:2] Other Poskim, however, are lenient even regarding measuring in weight. [Pesach Hadvir 1 p. 196, Vol. 3 306:15, brought in Kaf Hachaim ibid; Rav SZ”A ibid; Or Letziyon ibid; Yechaveh Daas ibid] Rav Oavdia Yosef was accustomed to weigh a few of the Matzos on the night of Pesach on a mechanical scale, and to then distribute the rest of them according to estimation. [Heard from his son Rav Yitzchak Yosef Shlita]
 The reason: As one is able to measure them before Yom Tov. [Admur 506:1]
 Admur 308:88 “Now, one may not claim that it is permitted [to move this vessel] being that it is a measurement done for a Mitzvah, as one learns through this vessel, being that the [Sages] only permitted measuring for a Mitzvah purpose when the measurement itself contains a Mitzvah, such as to measure a Mikvah [if it has enough water] and the like. However here the measurement itself has no concept of a Mitzvah, as the learning that he accomplishes through it [is not valid] as how can one depend his learning on something that is prohibited, and because of this it will be permitted [to use].”; M”A 308:78; M”B 308:167
 The contradiction in Admur: Admur 306:18 and 308:88 rules that it is permitted to measure for the sake of a Mitzvah, seemingly contradicting the above rulings of Admur ibid regarding Yom Tov. In truth, however, one can answer that the two rulings refer to different cases, as only if one could not have done the measuring before Yom Tov is it permitted to measure on Yom Tov, and that is the ruling in 306:18, while the other rulings refer to a case that on. Alternatively, one can answer that only a Medida Shel Mitzvah is Mutar on Shabbos and not a Medida that is commonly done during the week, and he simply intends to do so for a Mitzvah. [See Marei Mekomos Utziyunim on 456 and 506; Hearos Ubiurim Ohalei Torah 733 p. 51; See Minchas Dovid 4:82]
 Implication of Admur ibid regarding Shabbos who states “Medida Shel Mitzvah, versus Yom Tov in which Admur states Miskavein Lemitzvah
 Implication of Admur ibid and ibid regarding Yom Tov that if one could not have done so before Yom Tov then it may be done on Yom Tov; Marei Mekomos Utziyunim on 456 in answer to contradiction; M”B 618:21 in name of Achronim; Kaf Hachaim 486:3; 618:37, 45; See Kinyan Torah 5:22; Piskeiy Teshuvos 306:25
 See Kaf Hachaim 486:3; Minchas Dovid 4:82
 Admur 306:18; Michaber 306:7; Rambam Shabbos 24:5; Mishneh Shabbos ibid
 Admur 306:18; M”A 306:16; Elya Raba 306:20; Tosefes Shabbos 306:21; Kaf Hachaim 306:61
 The reason it is permitted despite the fact that the priests can simply leave the room without doing the measurement: Now, although the priests can simply leave the room next door and go into another room [without needing to do any measurement], nevertheless, it is permitted to measure the hole and since one is measuring measurements of Torah it does not appear like a mundane act. [Admur ibid; M”A 306:16]
 Admur 306:18; Michaber 306:7; Tur 306; Ravayah 202; Maharam Merothenberg 512; Hagahos Maimanis Shabbos 24:4; Elya Raba 306:21;See Kaf Hachaim 306:65
 Admur ibid; 307:32; See Michaber Y.D. 179:8; Shach 179:8
 See Piskeiy Teshuvos 306:25 [he permits even if could have been done before Shabbos and Yom Tov, however, according to Admur since we cannot define this as Medida ZShel Mitzvah, therefore it is only permitted if it could not have been done beforehand.]
 Or Letziyon 2:25-2
 Admur 323:10; M”A 323:14; Terumos Hadeshen 54; Erech Hashulchan 306:2; P”M 306 A”A 16; M”B 306:35; 323:37; Kaf Hachaim 306:62; 323:62
Other opinions: Some Poskim rule that it is forbidden to measure if an Issur is nullified in 60x and one must use estimation. [Beis Yehuda 29]
 Koveitz Teshuvos Rav Elyashiv 1:50
 Pesach Hadvir 1 p. 196, Vol. 3 306:15; Rav SZ”A in SSH”K 29 footnote 103; Or Letziyon 2:25-2; Yechaveh Daas 1:16
 Kaf Hachaim 306:63 based on M”A 500:4 from where it is proven that weighing something is more severe than measuring; Kinyan Torah 5:22