Query to retrieve SQL Server login password length
I think, your corporate security meant by week passwords. One way of doing that (without any third-party tools) with help of in-built function PWDCOMPARE, but for this you need to have real week-passwords list available perhaps in database table from where every password looked-up and compared with SQL Login hashes one-by-one. following is the example:
Declare @pwText nvarchar(128);
Declare @WeekPassword_List table (pw nvarchar(128));
Declare @WeekPasswords_Active table (login_name sysname, pw nvarchar(128));

insert into @WeekPassword_List
values 
('password'),
('passwordpassword'),
('password123'),
('P@ssw0rd'),
('Pa55word'),
('Pa55w0rd'),
('Temp@password'),
('Temp123'),
('temp123'),
('temp@123'),
('Temp@123'),
('123'),
('1234'),
('123456'),
('12345678'),
('');

while exists (select 1 from @WeekPassword_List)
begin 
    SET @pwText = (select top 1 pw from @WeekPassword_List);

    INSERT INTO @WeekPasswords_Active
    SELECT name, @pwText
    FROM   sys.sql_logins
    WHERE  Pwdcompare(@pwText, password_hash) = 1;

    DELETE FROM @WeekPassword_List where pw = @pwText;
end 

select * from @WeekPasswords_Active;