I was going through a discussion thread over at duolingo [(**"How to use El and La in Spanish"**)](https://www.duolingo.com/comment/2166946), when I came upon the following question:

>**Anyone know the percentage of Spanish nouns ending in -a that are not feminine? 5%? 10%? Or is it just 1%?**

It made me wonder if someone might have answered this question here at Spanish StackExchange, but after going through several pages, the closest answer I found (punctuation edited) appeared as follows

>**... 95% of the cases, female gender ends with an -a ...**

in the following thread [(**"Beyond memorisation and time, how can you master Grammatical Gender in Spanish? [closed]."**)](https://spanish.stackexchange.com/questions/15788/beyond-memorisation-and-time-how-can-you-master-grammatical-gender-in-Spanish)

From this, I could surmise that 5% of nouns ending in -a are masculine.  However, since the user who wrote that doesn't cite any source, I have to wonder if that is just a rough guess.  **Is there anything more scientific that someone could provide on the percentage of nouns ending in -a that are masculine and the percentage ending in -o that are feminine?**

**Also, while I'm on the subject, does anyone know what percentage of Spanish nouns are feminine and what percentage are masculine (regardless of ending)?**