In modern times what percentage of monks are female? In the question When were women first welcomed into Buddhist orders? we learn that woman have been becoming monks for a long time.  In modern times (circa 2014 CE) what percentage of monks are female?
In reply to "what percentage of Buddhist monks are female?" -

In Korea, the number of bhikkhus and bhikkhunis is very similar.  In Taiwan, the numbers of bhikkhunis now substantially surpass the number of bhikkhus.  I am not sure about Vietnam.

In the Theravada Buddhism of Southeast Asia, with the Bhikkhuni Sangha in the early stages of a revival and not yet State supported, the numbers of bhikkhunis are growing, but still much less than the numbers of bhikkhus. In Sri Lanka, there are now more than 2000 Theravada bhikkhunis, far more than anywhere else in the world.  In Thailand, there are less than 200 bhikkhunis, as compared to around 200,000 bhikkhus. In Theravada Buddhism in "the West" (in Australia, the United States, Canada and Germany combined), there are also less than 200 bhikkhunis. 

Here in Northern California, there are more Theravada bhikkhuni viharas than in any other state or region in North America.  In this region there are ~60 Theravada bhikkhu temples (at last count) and 4 Theravada bhikkhuni viharas and hermitages. That's a 400% increase in bhikkhuni viharas in the past 5 years.