how to get mysql row size in GB

Just ended up with calculating the size of MySQL table in GB with the following query.

SELECT (data_length+index_length)/power(1024,3) tablesize_gb FROM information_schema.tables WHERE table_schema='db' and table_name='tablename'

Is it possible to get the size of a MySQL row in GB.

Or how to get the avg row size for the table in GB.