Both 二倍 and 两倍 mean "double". I'm wondering if there's any distinction between the two, e.g. with respect to grammar, or when to use which. (There is ordinarily a difference in usage between 二 and 两.)
Question: Is there any distinction between 二倍 and 两倍?
It's not mentioned on the Chinese Grammar Wiki page Expressing "multiples" with "bei".
This question is not a duplicate of When to use 一倍 vs 两倍 nor Saying 'doubled' in Chinese 一倍 vs 两倍 which ask about 一倍, while this question asks about 二倍.
They are exactly the same. Maybe, 两倍 is used more frequently than 二倍, but I don't have actual data to support it. It's just my impression.
In short, the character 两 often precedes a quantifier, while 二 does not. In ordinary life, we prefer 两倍/个/斤 to 二倍/个/斤.
However, when it comes to science and technology, 二 is preferred to 两. There is a jargon 二倍体(diploid) but 两倍体 does not exist.
If you focus on the usage of "double" only, 二倍 and 两倍 are the same, but 两倍 is more standard and common usage.
Strictly speaking, 二倍 is very nonstandard, it could be considered wrong in some cases.
二倍 could also be used in Cantonese meaning two times of something.
E.g. 卖出二倍的价钱-selling at two times the price
两倍 is used in Mandarin.
E.g. 两倍价钱-two times the price
两倍 is more often used than 二倍，because "二" sometimes means "stupid". Like “不要这么二！” means "don't be stupid".
the same, just a habit. in number we use 一二三四五六七八九十. but for thing we used to use 兩個、兩隻、兩張、兩百、兩萬
funny example 222,222,222
we used to call it 兩億兩千兩百二十二萬兩千兩百二十二
if you can't remember, always use 二 is fine
二倍 is more formal. eg. （in a government annual report）由于一系列利好政策，今年我市税收达到去年的二倍。
两倍 is more oral. The examples is too many. 我的饭量是你的两倍。 这支基金净值已经增长了两倍。
The meanings are equal actually because 2 = 两.
Question: Is there any distinction between 二倍 and 两倍?
It actually comes down to situational preference and the distinction is marginal at best.
Other contributors have already made some pointers.
However, I just wish to add that:-
(1) when making a general dimensional comparison, 两倍 is preferred; such as 两倍大, (twice as big), and 两倍多, (more than double)
(2) Also 两 is preferred when it involves an approximation without quantification when things are figuratively "doubled", like, 他眼睛比我的大两倍, (his eyes are twice as big as mine)
(3) 二倍 is preferred when some quantifiable comparison is made, like, 今天的收入涨幅了二倍，(today's income increased by two times) because 倍 by itself means "times" as in "how many times" something has increased by.
But, in most cases, the two words are interchangeable and any distinction could be a matter of preference.
