It is forbidden on Yom Tob to measure flour or other ingredients in a measuring cup. When preparing a recipe on Yom Tob, one must measure ingredients with "Umed Ha’da’at," a rough estimate, but it is forbidden to make a precise measurement. One may use a measuring cup, but only for making a rough estimate, and not for precise measuring. This applies to rice, as well. Likewise, if one is preparing meat, it is forbidden to make a precise measurement of volume or weight. It is forbidden to measure or weigh with a utensil, or by weighing the food against something else.
However, Halachic authorities make an exception for spices, such as salt and pepper. When it comes to other ingredients, using a bit more or a bit less than one ideally wants would not ruin the dish. When it comes to spices, however, too much or too little seasoning can ruin the food and make it inedible. Therefore, it is permissible to make a precise measurement of spices when cooking on Yom Tob. It should be noted, however, that the Magen Abraham (Rabbi Abraham Gombiner, Poland, 1635-1682) limits this Halacha to those who customarily make precise measurements of seasoning. If a woman normally adds spices based on rough estimates, without measuring precisely, then she may not measure the spices on Yom Tob.
On Pesah, it is permissible to measure wine, Masa and Marror to determine how much one must eat/drink to fulfill the Misva. The Sages did not apply this prohibition of measuring to measuring that is needed for a Misva, so measuring for this purpose is permissible on Yom Tob.
Summary: It is forbidden to make precise measurements of food ingredients when cooking on Yom Tob; foods must be measured with rough estimates, and not precise measurements. An exception to this rule is spices, which may be precisely measured if one normally makes precise measurements of spices when cooking. Another exception is measurements needed for a Misva, such as measuring the wine, Masa and Marror at the Seder to determine how must one must eat and drink.
