Normally, TeX uses a space and a third between sentences. But it's actually more complicated than that, because the amount of space can be stretched or shrunk

Normally, TeX uses a space and a third between sentences. But it's actually more complicated than that, because the amount of space can be stretched or shrunk to achieve text justification. More details are at: https://tex.stackexchange.com/a/4726 https://tex.stackexchange.com/a/4726