up to 500g parcel, own packaging is $7.20, that is the lower end of parcel rates.

I noticed this yesterday on Aust Post calculator.

It calculated the right rate for the small parcel measurements/weight (400gms) I entered - $7.20

But for a satchel recommendation it  came up with a 5kg one ($16.70). It does say recommended size is a guide only.

What help is that to someone who isn't familiar with satchel sizes? Why doesn't it recommend a 500g one?