Estimated volume weight or actual weight?

I will ship a package with Europe duty-free cargo line B to Sweden and I don’t want to ship more than 10kg in one haul (suggested?), do customs read the volume weight or the actual weight? Declared value will be about 17-21 dollars. Do you prefer to split in 2 parcels and is it enough to tell them to to that in the message box or do I need 2 different shipping? Many questions but first time, thanks!