Currently, the choices in the "Serving Size" area are limited to the options entered when the food item was created. If the MyFitnessPal team entered the item, the Serving Size field may contain multiple options, If another user entered the item there is typically only one choice.
However, by manipulating the "number of servings" value, you can log different serving sizes. So, if the serving size is 1 cup, and you use 3/4 of a cup, enter .75 as the number of servings. Some apps may present the option to enter fractions, as well as decimals.
The serving size options will also include a single-unit option: for example, an item created with a 10 ounce serving size will also offer a 1 ounce serving size. It may be helpful to choose this single-unit option, and then use the number of servings as a multiplier.
If you are looking for a different serving size (for instance, ounces instead of grams), examine some of the other items in the search results: one or more may include your preferred unit of measurement. We are looking into adding a feature to convert serving size choices in future updates.
If you find you are constantly adjusting the number of servings on a particular item, you may prefer to save your adjusted item as a meal for easier reference.
We also offer the option of creating a new food item with the portion size you would like.