Find the largest (byte size) 20 tables in GB in MySQL 5.x - taken from: https://www.percona.com/blog/2008/02/04/finding-out-largest-tables-on-mysql-server/

largest_tables.mysql

SELECT CONCAT(table_schema, '.', table_name),
       CONCAT(ROUND(table_rows / 1000000, 2), 'M')                                    rows,
       CONCAT(ROUND(data_length / ( 1024 * 1024 * 1024 ), 2), 'G')                    DATA,
       CONCAT(ROUND(index_length / ( 1024 * 1024 * 1024 ), 2), 'G')                   idx,
       CONCAT(ROUND(( data_length + index_length ) / ( 1024 * 1024 * 1024 ), 2), 'G') total_size,
       ROUND(index_length / data_length, 2)                                           idxfrac
FROM   information_schema.TABLES
ORDER  BY data_length + index_length DESC
LIMIT  20;

Updated:

SELECT table_name "Table Name", table_rows "Rows Count", round(((data_length + index_length)/1024/1024),2) as megabytes FROM information_schema.TABLES WHERE table_schema = "app" order by megabytes asc;