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Run from a mysql root console:

SELECT table_schema AS "Database name", SUM(data_length + index_length) / 1024 / 1024 AS "Size (MB)" FROM information_schema.TABLES GROUP BY table_schema;

This will get you a result like the following:

+----------------------+--------------+
| Database name        | Size (MB)    |
+----------------------+--------------+
| information_schema   |   0.00781250 | 
| mysql                |   0.61204815 |
| project1_development | 281.59375000 |
| project1_test        |   7.29687500 |
| project2_development |   2.65625000 |
| project2_test        |   0.15625000 |
+----------------------+--------------+