database_transaction_log_bytes_used for 1 row is greater than the actual row size

As per the article

http://sqlskills.com/BLOGS/PAUL/post/How-expensive-are-page-splits-in-terms-of-transaction-log.aspx

CREATE DATABASE PageSplitTest;
GO
USE pagesplittest;
GO

CREATE TABLE BigRows (c1 INT, c2 CHAR (1000));
CREATE CLUSTERED INDEX BigRows_CL ON BigRows (c1);
GO

INSERT INTO BigRows VALUES (1, 'a');
INSERT INTO BigRows VALUES (2, 'a');
INSERT INTO BigRows VALUES (3, 'a');
INSERT INTO BigRows VALUES (4, 'a');
INSERT INTO BigRows VALUES (6, 'a');
INSERT INTO BigRows VALUES (7, 'a');
GO

BEGIN TRAN
INSERT INTO BigRows VALUES (8, 'a');
GO

SELECT [database_transaction_log_bytes_used] FROM sys.dm_tran_database_transactions
WHERE [database_id] = DB_ID ('PageSplitTest');
GO

database_transaction_log_bytes_used
-----------------------------------
1228

Why database_transaction_log_bytes_used=1228, while it should be 1000 bytes the size of 1 row?

Regards,

Manish