Diamension of Parcel allowed on surface mail for international sending.

Hi,

I intend to pack 30 items(each 1.3kg) measuring 18.5cm x 11cm x 6cm into a parcel for international sending from china to singapore. I understand that china post sell boxes for parcel sending. Do u know the dimensions of the bigger box for my needs?

Or can i send using my own cardboard boxes?

Thanks