This will show you the bytes in use in each of the transaction logs in the databases on the system:-

USE [master];

GO

SELECT

DB_NAME(database_id) AS [Database],

SUM(database_transaction_log_bytes_used_system) AS [System Bytes Used],

SUM(database_transaction_log_bytes_used) AS [Bytes Used]

FROM

sys.dm_tran_database_transactions

GROUP BY

DB_NAME(database_id)

ORDER BY

DB_NAME(database_id) ASC