The significant role played by Zakah in the circulation of wealth within the Islamic society is also played by the Sadaqah al-Fitr. However, in the case of Sadaqah al-Fitr, each individual is required to calculate how much charity is due from himself and his dependents and go into the community in order to find those who deserve such charity. Thus, Sadaqah al-Fitr plays a very important role in the development of the bonds of community. The rich are obliged to come in direct contact with the poor, and the poor are put in contact with the extremely poor. This contact between the various levels of society helps to build real bonds of brotherhood and love within the Islamic community and trains those who have, to be generous to those who do not have.
Zakah al-Fitr is only Wajib for a particular period of time. If one misses the time period without a good reason, he has sinned and can not make it up. This form of charity becomes obligatory from sunset on the last day of fasting and remains obligatory until the beginning of Salah al-‘Eid’ (i.e. shortly after sunrise on the following day). However, it can be paid prior to the above mentioned period, as many of the Sahabah [companions of the Prophet ﷺ] used to pay Sadaqah al-Fitr a couple days before the `Eid. Nafi reported that the Prophet’s companion Ibn `Umar used to give it to those who would accept it and the people used to give it a day or two before the `Eid. Ibn `Umar reported that the Prophet (peace be upon him) order that it (Zakah al-Fitr) be given before people go to make the Salah (al-‘Eid). And Ibn `Abbas reported that the Prophet (peace be upon him) said, “Whoever gives it before the Salah will have it accepted as Zakah, while he who gives it after the Salah (will not, for it will only be considered as) ordinary charity.”  Therefore, one who forgets to pay this Zakah al-Fitr on time should do so as soon as possible even though it will not be counted as Zakah al-Fitr.
The amount of Zakah is the same for everyone regardless of their different income brackets. The minimum amount is one Sa` (two handfuls) of food, grain or dried fruit for each member of the family. This calculation is based on Ibn `Umar’s report that the Prophet (peace be upon him) made Zakah al-Fitr compulsory and payable by a Sa` of dried dates or a Sa` of barley. The Sahabi, Abu Sa`id al-Khudri said, “In the Prophet’s time, we used to give it (Zakah al-Fitr) as a Sa` of food, dried dates, barley, raisins or dried cheese”. 
*A Prophetic sa’ ( صاع ) is not a weight measurement. It was and still is a measurement of volume, similar to the size of a large salad bowl. It is made up of four mudds, and a mudd ( مد ) is a smaller container, close to the size of a small salad bowl. To be precise, a Prophetic mudd in modern volume measurements is .75L (or 750mL), which means that a sa’ is three liters.
Note: In today’s most commonly used scale of measurement of commodities are in kilogram (Kg.), which in this case – one sa’ is approximately between 2.5 Kg t 3.0 Kg. In the middle east, there are ready-made packs of rice in 3.0 Kg/Pack of rice which are intended for individual payee of Zakat al-Fitr.
 Collected by al-Bukhari – Arabic/English, Vol. 2, p.339, no. 579
 Collected by ibn Majah – English Trans., Vol. 3, Book 8, Hadith 1827 – rated Hasan
 Collected by al-Bukhari – Arabic/English vol. 2, p. 340, no. 582
 article of Dr. Bilal Philips in Zakat al-Fitr