Stolen from TablePlus Blog, Cool product check it out here!

Size of all tables:

SELECT 
     table_schema as `Database`, 
     table_name AS `Table`, 
     round(((data_length + index_length) / 1024 / 1024), 2) `Size in MB` 
FROM information_schema.TABLES 
ORDER BY (data_length + index_length) DESC;

Size of an specific table:

SELECT
	table_name AS `Table`,
	round(((data_length + index_length) / 1024 / 1024), 2) `Size in MB`
FROM information_schema.TABLES
WHERE
	table_schema = 'db_name'
	AND table_name = 'table_name';