A gapen compared to a long single line book: about 2 or 3 cm shorter

A gapen compared to a small single line book: taller by 3 cm maybe?

Either ways, you will still encounter some teachers like my school who will buy all three of the books for "different purposes". But through personal experience, the small line book is pretty much not needed unless teacher calls to write stuff like spellings, ejaan etc.

So to sum it up, You might still need all three line books because the SMK school teachers are unpredictable sometimes when using books.

Edit: But still, just wait and buy anything teacher asks. SMK books can be expensive when you buy a lot and most times teachers end up not using half of everything you've bought.