It is forbidden to measure on Yom Tov.^[1] This applies whether with one’s hands or with a measuring tape [or with a vessel^[2]].^[3] This applies whether for business or personal related purposes.^[4] Thus one who is making Challah on Yom Tov may not measure the amount of flour being used even if one intends to do so for the sake of knowing if it is obligated in Hafrashas Challah.[5] [This applies whether one uses a mechanical or digital measuring item or weight machine.^[6] Likewise, one may not measure his weight or height on Shabbos.^[7] Accordingly, all instruments which are designated for measuring are Muktzah on Shabbos in the status of Keli Shemilachto Leissur, such as a ruler, measuring tape, measuring stick, scales.^[8]]

Measuring spices:^[9] It is permitted to measure spices on Yom Tov to see how much spice one’s food needs, if one commonly does so also during the week. [One may even use a measuring spoon, although he should place slightly more or slightly less than needed.[10]] If however one does not commonly measure the amount of spice added to a food, then he may not measure it on Yom Tov.

May one measure Shiureiy Mitzvah on Yom Tov? One may not measure the Shiurim of weight or volume on Yom Tov itself.^[11]Thus one is to measure the amounts before Yom Tov begins.^[12] If one did not do so, then one is to eat a lot of Matzah and Maror to the point he is certain that he ate Keshiur.^[13] Nonetheless, some are lenient to allow measuring on Yom Tov itself.^[14] If it was not possible to measure the amounts before Yom Tov, such as his Matzos or wine only arrived on the night of the Seder, then seemingly it may be measured on Yom Tov according to all.^[15]

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[1] The reason: As this is considered a mundane act and desecration of Shabbos [i.e. Maaseh Chol Vezlizul Deshabbos]. [Admur 306:18; 323:1; 324:2; 506:1 regarding Yom Tov; M”A 306:16; Tosafus Shabbos 126b] As it appears like one is selling. [Admur 506:1; Rashi Beitza 29a] See Chasam Sofer Shabbos; Keren Ledavid 72; Piskeiy Teshuvos 306:24

[2] Admur 323:1

[3] Admur 306:18; 500:1 regarding weight

[4] Admur 324:2; 323:1; 506:1 regarding Yom Tov

[5] Admur 456:9

[6] Piskeiy Teshuvos 306:24

[7] Piskeiy Teshuvos 306:24 footnote 162

[8] Piskeiy Teshuvos 306:24 footnote 167

[9] Admur 504:9

[10] Bach; Elya Raba 504:1; P”M 504 M”Z 1; Kitzur SHU”A 98:9; M”B 104:3; Nitei Gavriel 7:5

[11] Admur 456:9; 506:1 [based on Michaber 506:1; Shmuel Beitza 29a]that this applies even when measuring for the sake of a Mitzvah, if one could have measured it before Yom Tov; Kaf Hachaim 486:3; See Kinyan Torah 5:22; The following Poskim rule that one is not to Lechatchila measure on Yom Tov, and it is hence to be done before Yom Tov: M”B 618:21 in name of Achronim; Piskeiy Teshuvos 306:25

The reason: As one is able to measure them before Yom Tov. [Admur 506:1]

Other rulings of 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. 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 one could have measured before Yom Tov, as explicitly stated by Admur in 506:1.

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; 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 Yom 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, 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]

[12] Kaf Hachaim 486:3; 618:37, 45; M”B 618:21 in name of Achronim; Piskeiy Teshuvos 306:25

[13] Kaf Hachaim 486:3

[14] See other opinions in previous footnotes!

[15] As rules Admur 306:18 and 308:88