Is one permitted to measure on Shabbos?

            One is prohibited to take measurements on Shabbos, even though in essence it does not involve a melacha, because it is a weekday activity (òåáãà ãçåì) and is disrespectful to Shabbos, [1] and therefore not permitted on Shabbos.

            What does this include?

            This includes weighing items on a scale (mechanical obviously), weighing oneself on a scale, using a tape measure or ruler to measure distances, using a measuring spoon, measuring with a scaled glass or bottle. It is forbidden to measure the volume of a certain liquid, and therefore one may not pour liquid into a baby’s bottle to know its volume.

Rav Shlomo Zalman Auerbach ztz”l is in doubt whether counting floor tiles to know the size of a room is a problem, when one knows the width of an individual tile and thus know the size the room. [2]

            Is one permitted to measure for the sake of a mitzvah?

            As mentioned, measuring on Shabbos is an issur d’rabanan because it is a weekday activity – òåáãà ãçåì. However, measuring for the sake of a mitzvah cannot be termed an òåáãà ãçåì because it is done for the sake of a mitzvah. [3]

            Do you have examples of such measuring?

            If milk fell into a pot of chicken soup, in order to eat the soup it must be sixty times the volume of the milk. One may estimate the volume of the soup and pasken accordingly. [4]

• A mikveh must hold a certain quantity of water: if there is doubt as to whether the mikveh contains sufficient water, one may measure the volume of water.
• Another case deals with purity. The halacha is that impurity emanating from a dead body can pass through a gap in the wall if the gap measures a tefach by a tefach. It is sometimes necessary to measure this gap in order to know whether cohanim may remain in the room adjacent to the dead body. One may use a tape measure or ruler and measure the gap on Shabbos.
• It is imperative that one make kiddush on a cup that holds a quarter of a lug of wine or grape juice. If one is in doubt as to whether the cup holds the required amount, one may measure it on Shabbos. A possible method is to use a baby’s bottle, which has the units written on it and fill the kiddush cup accordingly.
• One must eat a required amount of matza and maror on Pesach night and to know the correct amount, one may measure with one’s hand or with any other measuring instrument.
• One may not walk a distance of 2000 amos outside the town’s perimeter. A practical way to measure on Shabbos would be to count one’s steps, obviously depending on whether one knows how large one’s steps are. Accordingly one may walk that distance while keeping track of how far one is walking from the town.

            What about for the sake of a baby or for an ill person?

            The Mechaber says [5] that one may measure for the sake of the ill because it is considered measuring for a mitzvah. The Mishna Berura explains [6] that healing is a mitzvah and therefore measuring is part of the mitzvah.

• One may measure the quantity needed for medicine. This is true for powder, tablets and liquid.
• One may measure the amount of food and liquid required to be eaten on Yom Kippur in case of pikuach nefesh. Often it suffices to eat a small amount without having to eat a full amount and one may measure this amount when necessary.

A baby or child is considered in halacha as having a weak system and therefore one may measure the amount of powder needed to be placed inside the baby’s bottle etc.

            Why is “measuring time” not ossur (you look at your watch, don’t you)?

            The question is better than the answer. It is because one is not really measuring anything, one is merely calculating a spiritual factor. One could debate whether taking one’s temperature is the same thing, but irrespective, one may take one’s temperature on Shabbos when illness is an issue. [7]

            What about weighing oneself on Shabbos?

            Unless there is a medical reason, it is forbidden to weigh oneself on Shabbos. We already mentioned that a baby or child is different and if they indeed need weighing after a meal for health reasons it is permitted.

            What about looking at a barometer on Shabbos or at a room thermometer?

            Here again we can say that one is not really measuring anything physical, or even doing an action of measuring, and thus one may look at them on Shabbos.

It is worthwhile knowing that if one uses a measuring tool such as a measuring spoon and one is not meticulous that the measure be accurate, it may be used. [8] One should remember this and implement it whenever one is in doubt whether one is permitted to measure on Shabbos or not.

            What exactly is permitted on Shabbos, when buying a house in Eretz Yisrael?

  The gemora in Gittin 8b says that even though one is rabbinically prohibited to tell a gentile to violate an issur on Shabbos, nevertheless, when it comes to buying a house in Eretz Yisrael it is permitted. The case involved in the gemora concerns the person who had already purchased a house from a gentile, but the deed had not yet been certified in court. The gemora says that since it involves the mitzvah of yishuv Eretz Yisrael (settling the land of Israel) one may instruct a gentile to draw up the contract and have it certified in a gentile court. The only prohibition involved is àîéøä ìòëå"í (instructing a gentile) which may be waived in face of the mitzvah of yishuv Eretz Yisrael.