How can I tell something's size in Japanese?


I am learning Japanese and helping a Japanese person with English. (My English
is not very good, but she still wants me to help her.)

She needed to describe someone's personality and she used "big person". And I
didn't understand what she meant by that. I asked her what she meant by "big
person" and she said she meant "broad-minded person".  
So I told her using "big" for someone's personality is wrong. Then she asked
me why, I told her it's used for describing something's size, but she didn't
understand even though I told her several times.  
So I wanted to tell her the word that Japanese people use for describing
something's size.  
I searched for it on the Internet, but there are so many words that mean
"big".

So... I don't know which one to choose. I would be so happy if someone can
tell me which one I should use. Also, I am really curious why she used "big
person" instead of directly saying "broad-minded person". Is that a saying in
Japanese?




大きな/大きい are the most basic word that means "big". For the difference, see:
[What's the difference between 大きいケーキ and
大きなケーキ?](https://japanese.stackexchange.com/q/21611/5010)

In Japanese, 大きな人 and 大きい人 refer to either one's physical size or one's broad-
mindedness/capacity, depending on the context. You can say 体が大きな人 or 心が大きな人 to
avoid ambiguity. There are also other expressions that mean only one thing.
大柄な only means physically "large". 寛大な and 心が広い only mean "broad-minded". So
you can explain to her using these words and phrases.

The same is true for 小さな/小さい. 小さい人 means either a (physically) short person or
a petty-minded person, depending on the context.

By the way, English "big" can refer to an important person in a certain field
(cf. [Big Three](https://en.wikipedia.org/wiki/Big_Three)), but such people
are rarely referred to as 大きい人 in Japanese.

