Total population of Athens at that time was estimated at
300,000 .
Complete mobilization of all available manpower is usually
set at max of 20% of population giving Athens some
60,000 if all manpower was used.
At the battle of Marathon, Athens was able to muster only 10,000 and I would guess that was a maximum effort.That would indicate a population of 50,000 based on the 20% figure.
They only had 11,000 total as Plataea sent their entire army of 1000 to help. Sparta sent their army but they were delayed by a religious festival.