You could use SQL to get the database size. It wouldn’t be exactly the same as disk allocation, but it should be close.
SELECT
table_name AS `Table Name`,
table_rows AS `Row Count`,
ROUND(SUM(data_length)/(1024*1024*1024), 3) AS `Table Size [GB]`,
ROUND(SUM(index_length)/(1024*1024*1024), 3) AS `Index Size [GB]`,
ROUND(SUM(data_length+index_length)/(1024*1024*1024), 3) `Total Size [GB]`
FROM information_schema.TABLES
WHERE table_schema = 'homeassistant'
GROUP BY table_name
ORDER BY table_name
Above is for an installation on MariaDB. Adjust the database name (table_schema) as needed, or remove the WHERE clause entirely if all you have on that service is your Home Assistant schema.
You’d get something like the following (here produced using phpMyAdmin):
