Approximation of table size for MySQL cluster

Question

I want to make some approximation of table size for MySQL cluster.
Please read my reasoning and tell me, if I am right or am I making mistake somewhere.

I have simple table with PK (int) and additional column (int). In MySQL int = 4 bytes, so one row is about 12 bytes (4*2 for columns and 4 for PK index).
If I have for example 1'000'000 rows this will be 12'000'000 bytes ~= 11.5MB.
Am I right in this calculations? Can I store such table with so little space?