I only have experience with mainland Chinese families having 3 character names, however, my family only has 2 characters in our names. I saw a similar question acknowledging the difference between Hong Kong (3 characters) and mainland China (2 characters), but in my experience i've only seen mainly 3 character names for those from mainland China. I am curious to know if there is a cultural significance between having the extra character. What is the true norm?
In ancient times, China was a matriarchal society, and children followed their mother's family name by "姓" (女 = woman; 生 = born)
Most surname is one character word, two-character surname is rare in comparison
The family name of the child's father is "氏"
Sometimes later, China became a patriarchal society, but we still use the term 姓 or 姓氏 to refer to the family name passed down from the father's side of the family and single-character surname is in the majority
Before Tang Dynasty, 名 (given name) mostly consisted of one character. Two characters' names became popular after the Tang Dynasty until today
In modern times, two-character given names are still the majority, but single-character given names have become more common in Mainland China but not in Hong Kong or Taiwan
Two characters' full name (one for surname, one for given name) is not uncommon nowadays
Three-character name (one for surname, two for given name) is still the most common one
In the case of someone having a two-characters surname, four-character full name is more common for them (two for surname; two for given name)
Please reference Why is there such a difference between "first name" and "last name"?
People can have anywhere from 2-4 character names without being extremely unusual (1-2 characters in the family name and 1-2 characters in the given name). The majority of people have only one character for their family name, and those with two almost always have a two character given name as well.
So let's look at given names for those with a single character family name:
It is common for them to have 1 or 2 character given names. I don't think there is a specific logic for 1 vs 2 specifically, at least as far as meaning or significance etc. (maybe the name maker just didn't think of a single character name they liked or vise versa).
However, there are two factors I am aware of that make two character given names more likely:
It is extremely common for siblings (and sometimes cousins etc.) to share a "generation" character in their given names. For example the first character of the given name is both 寶. Depending on how traditional the family is this could be predetermined (from a poem etc.), chosen by a family elder or just by the parents themselves.
More recently 2 character given names are actually encouraged over 1 character given names for a very practical reason. It decreases the chance of someone else having the same name drastically and helps avoid identity confusion.
Just imagine this example (I am not using real numbers, 1,000 is completely arbitrary and only an exercise on the difference):
Let's say hypothetically there are 1,000 Chinese characters with a good name potential. Even if you combined them in all the different ways possible that's approximately 500,000 different names. So dozens, if not hundreds, of people in China would all have the same name at once, no matter how hard you try! In this way 1 character given names are definitely becoming less common (although they are far from gone.)
No, the one character or two characters given name has nothing to do with the cultural difference but the different choices of parents, often influenced by the circumstance at the birth of a child. For instance, one of my girlfriends is Shanghainese and was born in Guangdong Province, therefore her parents named her "李粵" to keep Guangdong(粵) in family memory. Or, name the newborn per the parents' expectation of the child after growing up, such as 張潔(wish her always maintain innocence), and 孫全(wish him a life full of completeness).
In 2020年全国姓名报告 published by Chinese government in 2020, there is a paragraph about this topic:
And the graph below shows the historical trend (red line for 3-character name percentage, blue for 2-charater):
In the old days, each generation in the clan often has a common character (字辈) in their names, so 2-character names were rare. For example, 孔繁A, 孔繁B, 孔繁C are "繁字辈". When this concept became diluted since reform and opening-up, 2-character names got more popular than before, but 3-character names were still the majority. Later, to avoid having the same name with too many people, 2-character names became less popular again. For example, there are about 300,000 people named 张伟.
Practically speaking, it has nothing to do with culture. Whether you'll have a 2-character first name or single character first name almost totally depends on your parents. However, it's true 3-character names are more likely to be unique and creative. If your family is the old-fashioned type(i.e., prefer to share a generation character to represent family identity), then 2-character first name becomes the only choice.
As for the difference between mainland and HK/Taiwan, I think it's reasonable to say the same rule applies. Eg. Ang Lee(李安) from Taiwan，Albert Leung(林夕）from HK
Now days 2~4 character names(family name + second name) are common. The family name（姓氏） often use 1~2 character and you can not change it easily. And the second name（名） use 1~2 character.
But in some ancient dynasties, 1 character second names are considered noble. If you read one of the Four Famous Novels, 《三国演义》, you may find most names in it are 2 character name, like 诸葛亮(family name is 诸葛, second name is 亮), 周瑜(family name is 周, second name is 瑜). They all use 1 character second name.
In fact, there are different norms in different periods.
For example, during the Three Kingdoms period, two characters were mainly used, but people in the Three Kingdoms period all had style name, such as “关羽”，surname is "关"，given name is "羽". And his style name is "云长". We can call him "关羽" or "关云长".
In modern China, Chinese people have generation names. As kyc said, all the people born in the same generation have the same generation name. Like 孔繁A, 孔繁B, 孔繁C.
However, with the development of civilization, naming has become more and more liberal and diversified. Modern people do not have to abide by the previous rules. Parents can choose names according to their own wishes. When they grow up, they can change their names if they are not satisfied. Two character, three character, or even four character names are available.