Determining Nvarchar length

Generally it is the same as for varchar really. The number is still the maximum number of characters not the data length.

nvarchar(100) allows 100 characters (which would potentially consume 200 bytes in SQL Server).

You might want to allow for the fact that different cultures may take more characters to express the same thing though.

An exception to this is however is if you are using an SC collation (which supports supplementary characters). In that case a single character can potentially take up to 4 bytes.

So worst case would be to double the character value declared.

From microsoft web site:

A common misconception is to think that NCHAR(n) and NVARCHAR(n), the n defines the number of characters. But in NCHAR(n) and NVARCHAR(n) the n defines the string length in byte-pairs (0-4,000). n never defines numbers of characters that can be stored. This is similar to the definition of CHAR(n) and VARCHAR(n). The misconception happens because when using characters defined in the Unicode range 0-65,535, one character can be stored per each byte-pair. However, in higher Unicode ranges (65,536-1,114,111) one character may use two byte-pairs. For example, in a column defined as NCHAR(10), the Database Engine can store 10 characters that use one byte-pair (Unicode range 0-65,535), but less than 10 characters when using two byte-pairs (Unicode range 65,536-1,114,111). For more information about Unicode storage and character ranges, see

https://docs.microsoft.com/en-us/sql/t-sql/data-types/nchar-and-nvarchar-transact-sql?view=sql-server-ver15