The saa during the time of the Prophet ﷺ was equivalent to one and a third mudd by your present-day mudd. It was increased during the time of Umar bin Abdul Aziz.
Azami 10672
Sahih
عن السائب بن يزيد قال
كان الصاع على عهد النبي ﷺ مدا وثلثا بمدكم اليوم، فزيد فيه في زمن عمر بن عبد العزيز.
Bukhari narrated it in the Book of Expiations for Oaths (6712), from Uthman bin Abu Shayba, who said, Qasim bin Malik Muzani narrated to us, Juayd bin Abdul-Rahman narrated to us, from Saaib, and he mentioned it.