Maha-bharata Adi Parva, Sangraha
An aksauhini is a whole army consisting of
109,350 foot soldiers,
“The Rishis said,
‘We have a desire to know, O son of Suta, what is implied by the term Akshauhini that hath been used by thee. Tell us in full what is the number of horse and foot, chariots and elephants, which compose an Akshauhini for thou art fully informed.’
‘One chariot, one elephant, five foot-soldiers, and three horses form one Patti; three pattis make one Sena-mukha; three sena-mukhas are called a Gulma; three gulmas, a Gana; three ganas, a Vahini; three vahinis together are called a Pritana; three pritanas form a Chamu; three chamus, one Anikini; and an anikini taken ten times forms, as it is styled by those who know, an Akshauhini. O ye best of Brahmanas, arithmeticians have calculated that the number of chariots in an Akshauhini is twenty-one thousand eight hundred and seventy. The measure of elephants must be fixed at the same number. O ye pure, you must know that the number of foot-soldiers is one hundred and nine thousand, three hundred and fifty, the number of horse is sixty-five thousand, six hundred and ten.
These, O Brahmanas, as fully explained by me, are the numbers of an Akshauhini as said by those acquainted with the principles of numbers. O best of Brahmanas, according to this calculation were composed the eighteen Akshauhinis of the Kaurava and the Pandava army.
Srimad-Bhagavatam 1 Canto
A solid phalanx of 21,870 chariots, 21,870 elephants, 109,650 infantry and 65,600 cavalry is called an aksauhini.