If a person cooks rice on Yom Tob, may he use a measuring cup so he can prepare a specific amount of rice? Halacha certainly allows one to cook on Yom Tob, but the question arises as to whether measuring is permissible as part of the process of food preparation.
The Sages forbade precise measuring on Yom Tob, but not making rough measurements. Therefore, it would be forbidden to use a measuring cup for the purpose of arriving at a precise amount. One may, however, use a measuring cup in order to roughly estimate an amount of rice. As long as ones intent is to arrive at a general estimate, and not to measure with precision, he may use a measuring cup to measure food. Certainly, it is permissible to use an ordinary glass, that does not have measurements, to determine the amount of rice that one wishes to prepare.
Furthermore, Hacham Ovadia Yosef rules that measuring is permissible for the purpose of a Misva. Some people have the practice of weighing Masa at the Seder to know precisely how much Masa they need to eat, and some Haggadot include tables and diagrams to help a person determine the amounts of Marror and other foods he needs to eat. These measurements are permissible on Yom Tob, because they are made for the sake of a Misva.
Summary: It is permissible to use a measuring cup on Yom Tob, provided that one makes a rough measurement, and does not measure precisely. It is permissible to make precise measurements on Yom Tob for the sake of a Misva, such as to determine the precise amount of Masa one must eat.
