The Shulchan Aruch writes (Siman 158) that a person who intends to eat a small amount of bread, less than a Ke'zayit, or 28 grams, need not wash his hands before eating. Even though he of course recites "Ha'motzi" even over this small quantity of bread, Netilat Yadayim (hand washing) is not required in this case. The Mishna Berura cites several authorities who agree to this ruling, but he adds that others disagree and require that in such a case one indeed washes his hands, only without a Beracha.
Therefore, if one plans on eating less than 28 grams of bread, he does not, strictly speaking, have to wash his hands, though it is commendable for him to be stringent and wash his hands without a Beracha.
Earlier in this same chapter, the Shulchan Aruch addresses a case of one who plans to eat a Ke'zayit or more, but less than a Ke'beitza – 56 grams, or 2 oz. In this case, he writes, one must wash his hands – according to all opinions – but he does not recite a Beracha. Washing with a Beracha is required only if one intends to eat 2 oz. or more of bread. Many people wash their hands with a Beracha on Friday night but intend to eat only a small piece of Challa. This is incorrect; a person who has no intention of eating a Ke'beitza does not recite a Beracha when he washes his hands.
If a person performed Netilat Yadayim with a Beracha, intending to eat a Ke'beitza of bread, but after eating a small amount he finds himself unable to eat any more, he is not required to force himself to continue eating. So long as when he washed his hands he had the intention of eating a Ke'beitza of bread, the Beracha is valid, even if ultimately he decides not to eat a complete Ke'beitza.
Although one is generally not required to perform Netilat Yadayim before eating Mezonot foods (such as cake, cookies and the like), nevertheless, one who plans on eating 230 grams of Mezonot must wash his hands before eating. Halacha deems the consumption of this quantity of Mezonot food a "Kevi'at Se'uda," an established meal, and therefore one must wash his hands before eating and recite the Beracha of "Ha'motzi" over the food. However, the authorities disagree as to whether one recites a Beracha over the Netilat Yadayim in such a case. Therefore, the Kaf Ha'chayim (Rabbi Chayaim Palachi, Rabbi of Izmir, Turkey, 19th century) rules that one should not recite a Beracha, in accordance with the general rule that one does not recite a Beracha if its requirement is subject to doubt.
Summary: One who intends to eat less than 28 grams of bread does not have to wash his hands, though it is commendable to wash in this case without a Beracha. One who intends to eat 28 grams or more, but less than 56 grams, such as one who intends to eat half a pita, must wash his hands, but without a Beracha. One washes with a Beracha only if he plans on eating 2 oz. or more of bread. One who washed with this intention but then finds it difficult to consume this quantity need not force himself to continue eating. One who plans on eating 230 grams or more of a Mezonot food must wash his hands without a Beracha and recite "Ha'motzi."
See Halichot Olam, Helek 1, page 315. Se Yalkut Yosef, Helek 3, page 17.
