Type different types of Mezonot
1. A cooked food Ė this is not considered bread-like and will always be mezonot.
2. A baked food Ė which is called Pas HaBah Bekisnin is similar to bread, and it is only mezonot when eaten as a snack, however if one eats the amount of a ďshiur suedaĒ then the Bracha is hamotzei. (We will define this term below)
1. Examples - borekas, hotdogs in dough shell, pretzels, crackers, biscuits, (matzah for Sephardim), and cake.
3. If pancakes are fried with in only as much oil is needed to prevent it from burning then it is considered a baked food. However, if it is fried with a small amount of oil (more than necessary to prevent burning but less than deep fried) thereís a dispute whether itís considered cooked or baked and so one if one has a shiur seuda of these type of pancakes one should first make HaMotzei on regular bread.
Shiur Seudah For Ashkenazim
Whenever one eats the amount of Shiur Sueda (amount of a meal) of Pas Haba Bikisnin one should wash, say Netilat Yadayim, Hamotzei, and Birkat HaMazon. How large is the Shiur Sueda? Some poskim say that it is 4 KeBaytzim, while others say that itís the amount an average person regularly eats for a meal. To avoid dispute one should eat less than 4 KeBaytzim and make Mezonot or eat more than the average meal and make HaMotzei. After the fact, if one did eat between these two amounts then if one isnít full one should make Al HaMichya and if one is full one should make Birkat HaMazon.
To clarify the second opinion, itís clear that the average meal varies from country to country and generation to generation. Rather the amount of an average meal depends on the amount normally eaten by people in his natural age group (because elderly people eat a different amount from teenagers and teenagers from children) of the same gender (because woman eat a different amount from men).
If one ate Pas HaBah Bekisnin together with foods that are normally eaten in a meal (such as meat, fish, eggs, etc.) and one ate an amount of Pas HaBah Bekisnin equal to the amount of bread normally eaten in a meal then all of these foods count towards the Shiur Seudah. Some say that the other foods eaten in the meal are counted towards the total only if one already ate 4 Kebaytzim of Pas HaBah Bekisnin besides the other foods, while others say that even if one only has one Kezayit of Pas HaBah Bekisnin together with the amount eaten in a meal of other meal foods one should make HaMotzei. According to this second opinion if a person at a wedding is interested in avoiding washing and substitutes crackers for bread then since the crackers and other foods amount to a Shiur Sueda one would have to wash and make HaMotzei on the crackers.
In terms of timing, all food thatís eaten during a meal is included as long as one kezayit of Pas HaBah Bekisnin is eaten within Kedi Achilat Pras (4 minutes).
Amount of an average meal
The Shiur Seuda is an objective amount. Nonetheless, one can easily calculate the amount of the average meal by knowing oneís personal average amount of a meal as long as one is a normal eater. If however, you know you eat more or less then most people do then one canít judge the average meal by yourself. 
If you eat less than most people do even if you personally are full, don't betch. If you eat more than most people do and are still not full you should bentch.
Sephardim hold that like the opinion which says that the Shiur Seudah is either 3 or 4 KeBaytzim. In order to avoid dispute one should eat less than 3 KeBaytzim and make Mezonot or more than 4 KeBaytzim and make Hamotzei.
Sephardim hold that the other foods one eats together with the Pas HaBah Bekisnin donít count towards the amount of eating the Shiur Seudah.
Size of a Kazayit
1) Many Sephardim go by weight, while others go by Volume and both are acceptable and each should keep their own minhag.
 Shulchan Aruch 208:2, Chaye Adam 54:2, Halachos of Brachos (chap 27, pg 481-3)
 Vezot HaBracha (chap 4, pg 26)
 Halachos of Brachos (pg 495)
 Vezot HaBracha (chap 4, pg 26-7)
 Halachos of Brachos (chap 27, pg 493) based on Mishna Brurah 168:56
 Shulchan Aruch 168:6
 Mishna Brurah 168:24
 Halachos of Brachos (chap 27, pg 488-9)
 Biur Halacha 168:6 DĒH Af Al Pi, ShĒt Igrot Moshe OC 3:33, Halachos of Brachos (chap 27, pg 487-8, note t and 24.1)
 Halachos of Brachos (chap 27, pg 490)
 Vezot HaBracha (chap 4, pg 32) quoting Rav Vosner and Rav Shlomo Zalman
 Vezot HaBracha (chap 4, pg 32) quoting Rav Sheinburg, inferring it from Rav Moshe, and quoting Rav Elyashiv who was concerned for this opinion
 Igrot Moshe 3:32, Halachos of Brachos (chap 27, pg 491)
 Yalkut Yosef (Birkat HaMazon pg 130 and 133), Vezot HaBracha (chap 4, pg 27)
 Vezot HaBracha (chap 4, pg 30)
 Shulchan Aruch 168:6
 Yalkut Yosef 168:8-9
 Yalkut Yosef (Birkat HaMazon pg 133)