It is permissible to pay zakaat al-fitr in the form of flour
Question

Is it permissible for a person to pay zakaat al-fitr in the form of flour?.
Praise be to Allah.Zakaat al-fitr must be given in form of the people’s staple food. Based on this, there is nothing wrong with giving it in the form of flour. 
Ibn Qudaamah (may Allaah have mercy on him) said in al-Mughni (2/357): It is permissible to give flour. This was stated by Ahmad. End quote. 
Abu Dawood (618) narrated from Abu Sa’eed al-Khudri (may Allaah be pleased with him) that they used to give a saa’ of flour for zakaat al-fitr, but this is a da’eef (weak) hadeeth which was classed as such by Abu Dawood and others. See: Irwa’ al-Ghaleel (848). 
The fact that the hadeeth was classed as da’eef does not mean that it is not permissible to give flour, because what is required, as stated abode, is to give what the people eat as their staple food. Hence Ibn al-Qayyim (may Allaah have mercy on him) said in I’laam al-Muwaqqi’een (3/12) after confirming that zakaat al-fitr should be given in the form of the people’s staple food, whatever it is: Based on that, it is acceptable to give flour, even if it is not mentioned in the saheeh hadeeth. End quote. 
The view that it is permissible to give flour for zakaat al-fitr is the view of Abu Haneefah and Ahmad (may Allaah have mercy on them), and it was the view favoured by Shaykh al-Islam Ibn Taymiyah. Among contemporary scholars it was viewed as most correct by Shaykh Ibn ‘Uthaymeen. 
The scholars – such as Shaykh al-Islam Ibn Taymiyah in Majmoo’ al-Fataawa (25/69) and al-Mardaawi in al-Insaaf (3/180) – have drawn attention to the fact that flour must be given by weight, i.e. equivalent to the weight of a saa’ of grain, because a saa’ of flour may be less than a saa’ of grain, so if a person gives a saa’ of flour it may be less than a saa’ of grain, and that is not permissible. 
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said in al-Sharh al-Mumti’ (6/179): If he gives a saa’ of wheat or barley flour, that is acceptable, but that is based on the idea that what counts with regard to flour is weight, because when grains are ground, they become less dense, so a saa’ of flour is nearly one-sixth less than a saa’ of grain. End quote. 
And Allaah knows best.