Para saber el espacio que ocupa una base de datos podemos usar esta consulta
SELECT table_schema "DATABASE", SUM( data_length + index_length ) FROM information_schema.tables WHERE table_schema != "information_schema" GROUP BY table_schema
O para verlo un poco más bonito
SELECT table_schema "DATABASE", CONVERT( SUM( data_length + index_length ) /1048576, DECIMAL( 10, 2 ) ) "SIZE (MB)" FROM information_schema.tables WHERE table_schema != "information_schema" GROUP BY table_schema
Como siempre espero que os sirva