A total of twelve thousand men and women fell that day--all the people of Ai.

Deuteronomy 20:16
However, in the cities of the nations that the LORD your God is giving you as an inheritance, you must not leave alive anything that breathes.

Joshua 8:24
When Israel had finished killing all the men of Ai who had pursued them into the field and wilderness, and when every last one of them had fallen by the sword, all the Israelites returned to Ai and put it to the sword as well.

And so it was, that all that fell that day, both of men and women, were twelve thousand, even all the men of Ai.