Q. We learned recently on the Daf about not having false weights and measures. How about having them at home not for commercial purposes but just for preparing foods, or weighing oneself etc.?
A. The Torah teaches us (Devarim 25:13-15), “You may not have a large weight and a small weight in your purse; you may not have a large measure and a small measure in your house. You must only have full and righteous weights and full and righteous measures.”
Sefer HaChinuch (Mitzvah 602) writes “We are prohibited from keeping false weights and scales in our homes, even though we do not do business with them, lest they be a stumbling block before us.
This prohibition is likewise ruled by the Rambam (Laws of Theft 7:3): “One who keeps an imprecise measure or weight in his home or store transgresses a negative commandment.” The Shulchan Aruch (Choshen Mishpat 231:3) similarly records that possession alone is a transgression. The above is based on the Talmud (Bava Basra 89b) that extends the prohibition beyond the grocer: “Rabbi Yehudah said in the name of Rav: It is forbidden to keep an imprecise measure in one’s house, even if it is made into a bedpan.”
The above would prohibit the use and even possession of everyday scales and measuring devices found in homes: such as baby balances, bathroom scales, food scales, tape measures, baby bottles with volume markings, and so on. Many of these devices are imprecise to begin with, and the inaccuracy often grows over time. It seems unlikely that such a widespread and common practice could involve even a Torah prohibition.
However, Kesef Hakodoshim (231: 3) rules that the prohibition applies only to measures and scales that can and would occasionally be used for commercial purposes.
Minchas Shlomo, (3: 106), finds a possible reason for leniency in the ruling of the Talmud (Bava Basra 89b) and Rambam, (H. Geneiva 8:4) concerning locations in which the law requires that all commercial scales be stamped with a seal of approval. Under such conditions it is permitted to keep an inaccurate scale and measure, if it does not bear the stamp of approval.
Based on the above, Horav S. Z.Auerbach zt”l further writes that the same principle can be applied to everyday weights and measures, whose very form and image bears testimony to their imprecision. Just as the absence of an official stamp ensures that inaccurate measures are not employed for commerce, so the obvious appearance of a scale or measure as imprecise, is sufficient to permit keeping it.
Minchas Yitzchok (10: 149) also maintains that when a sign is written on a scale stating that it is not for commercial use, it is permitted. A similar ruling is to be found in Chashukei Chemed (Bava Metzia 61b) in regards to scales used for the separation of Terumos and Ma'asros.
Horav Shlomo Miller's Shlit”a opinion is similar to the above lenient rulings.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a