Question 12: If for paying Zakaat-ul-Fitr (obligatory charity paid before the Festival of Breaking the Fast) to a specific person, one takes a bag of rice with a label showing that the weight of the bag is 40 or 45 kilograms according to the measure of the producing company. Thus, it is taken without emptying and measuring it by means of Saa`, according to which every 3 kilograms are regarded as one Saa`. In case the weight of the bag is less than the required amount, one will add to it, but if it is more, it will be Sadaqah (voluntary charity). Is this permissible?
Answer: It is necessary to be sure of the measure of the bag, which one will give as Zakaat-ul-Fitr. It is not sufficient to depend on the label written on the bag or the random estimation that it equals such and such amount, because it may be of a lesser amount, thus one is not fully clear from the obligation of Zakaat-ul-Fitr… read more here.