the Fatwa Department Research Committee - chaired by Sheikh `Abd al-Wahhâb al-Turayrî
Zakât al-Fitr becomes due at the end of Ramadan. It is obligatory upon every person who has enough wealth to suffice him for the day and night of `Id.
The amount that should be paid is one sâ` of a staple foodstuff. That means food such as rice, corn, dates, wheat, etc. It should be given on behalf of oneself and every member of the family that one is liable to support.
This sâ` is a measure of capacity equivalent to four double-handfuls.
Sheikh Muhammad Al-Jibâlî wrutes in Celebrations in Islam:
The sâ` is a fixed measure of capacity or volume. It varied from one place to another; but the Prophet (peace be upon him) standardized it by stating: “Weights are to be employed according to the standards of Meccas; and capacity measures are to be employed according to the standards of Madinah.” [Sunan Abî Dâwûd]
Therefore, the amount should be measured according to the sâ` of Madinah, which is still available to this time. However, this measure is not accessible to most people. Because of this, many scholars have estimated it approximately to four full double-handfuls (i.e. with the hands put together) of an average man. [Refer to al-Nawawî in al-Majmu’]
This demonstrates that it is wrong to measure Zakat al-Fitr by weight, because the weight of one sâ` varies for different materials. However, if the relationship between weight and capacity is determined for a specific foodstuff, then the equivalent weight of one sâ` of that material may then be used for that particular food.
Al-`Uthaymîn, in his fatwâ on the matter mentions that the sâ` is four full double-handfuls and then goes on to say that scholars give an approximate weight value for rice to be roughly 2.1 kilograms and for dates to be roughly 2.04 kilograms.
And Allah knows best.
Source: Islam Today