How to get the size of a varchar[n] field in one SQL statement?

Suppose that I have a SQL table that has a varchar[1000] field called "Remarks".

I would like to craft a single SQL statement, which when executed, will return 1000, or whatever the size of the varchar field might be changed to in the future.

Something like SELECT size(Remarks) FROM mytable.

How do I do this?

select column_name, data_type, character_maximum_length    
  from information_schema.columns  
 where table_name = 'myTable'

On SQL Server specifically:

SELECT DATALENGTH(Remarks) AS FIELDSIZE FROM mytable

Documentation

For SQL Server (2008 and above):

SELECT COLUMNPROPERTY(OBJECT_ID('mytable'), 'Remarks', 'PRECISION');

COLUMNPROPERTY returns information for a column or parameter (id, column/parameter, property). The PRECISION property returns the length of the data type of the column or parameter.

[COLUMNPROPERTY documentation][1]

[1]: https://docs.microsoft.com/en-us/sql/t-sql/functions/columnproperty-transact-sql "COLUMNPROPERTY documentation"

This will work on SQL SERVER...

SELECT COL_LENGTH('Table', 'Column')

I was looking for the TOTAL size of the column and hit this article, my solution is based off of MarcE's.

SELECT sum(DATALENGTH(your_field)) AS FIELDSIZE FROM your_table

This is a function for calculating max valid length for varchar(Nn):

CREATE FUNCTION [dbo].[GetMaxVarcharColumnLength] (@TableSchema NVARCHAR(MAX), @TableName NVARCHAR(MAX), @ColumnName VARCHAR(MAX))
RETURNS INT
AS
BEGIN
	RETURN (SELECT character_maximum_length FROM information_schema.columns  
            WHERE table_schema = @TableSchema AND table_name = @TableName AND column_name = @ColumnName);
END

Usage:

IF LEN(@Name) > [dbo].[GetMaxVarcharColumnLength]('person', 'FamilyStateName', 'Name') 
			RETURN [dbo].[err_Internal_StringForVarcharTooLong]();

select column_name, data_type, character_maximum_length    
from INFORMATION_SCHEMA.COLUMNS
where table_name = 'Table1'

For t-SQL I use the following query for varchar columns (shows the collation and is_null properties):

SELECT
	s.name
	, o.name as table_name
	, c.name as column_name
	, t.name as type
	, c.max_length
	, c.collation_name
	, c.is_nullable
FROM
	sys.columns c
	INNER JOIN sys.objects o ON (o.object_id = c.object_id)
	INNER JOIN sys.schemas s ON (s.schema_id = o.schema_id)
	INNER JOIN sys.types t ON (t.user_type_id = c.user_type_id)
WHERE
	s.name = 'dbo'
	AND t.name IN ('varchar') -- , 'char', 'nvarchar', 'nchar')
ORDER BY
	o.name, c.name

For MS SQL Server this will return column length:

SELECT COL_LENGTH('dbo.mytable', 'Remarks') AS Result;