אורח חיים תרי״בOrach Chayim 612

Se’if 1א׳

הָאוֹכֵל בְּיוֹם הַכִּפּוּרִים כְּכוֹתֶבֶת הַגַּסָה, חַיָּב; וְהוּא פָּחוֹת מִכַּבֵּיצָה מְעַט, וְשִׁעוּר זֶה שָׁוֶה לְכָל אָדָם בֵּין לְנַנָּס בֵּין לְעוֹג מֶלֶךְ הָבָּשָׁן.

1. The Prohibition of Eating on Yom Kippur and related measurements and in it is 10 paragraphs. One who eats on Yom Kippur (an amount) like a large date is obligated (for punishment having transgressed the Torah prohibition) and it is little less that egg-size. This measurement is equal to all people where Nanas (who was small) or Og, the King of Bashan (who was a giant).

Se’if 2ב׳

כָּל הָאֳכָלִים מִצְטָרְפִים לְשִׁעוּר זֶה, אֲפִלּוּ מֶלַח שֶׁעַל הַבָּשָׂר וְצִיר שֶׁל יָרָק; אֲבָל אֲכִילָה וּשְׁתִיָּה אֵינָן מִצְטָרְפוֹת.

2. All eating combines to this measurement even salt on meat, and juice on vegetables, but eating and drinking do not combine.

Se’if 3ג׳

אָכַל, וְחָזַר וְאָכַל, אִם יֵשׁ מִתְּחִלַּת אֲכִילָה רִאשׁוֹנָה עַד סוֹף אֲכִילָה אַחֲרוֹנָה כְּדֵי אֲכִילַת פְּרָס, מִצְטָרְפִין; וְאִם לָאו, אֵין מִצְטָרְפִין.

3. (In the case of) one who eats, (pauses), and returns and eats (again) - if from the beginning of the first eating until the end of the last eating was (the time) in order to eat a slice of bread, it combines. If not, it does not combine.