Auto calculated EMS shipping rate from Korea to international on shopify

[smk_]

We are sending parcels to international customer with EMS service but they don't have auto calculated shipping fee system on shopify, so it is way to hard filling it one by one.

Moreover EMS fee will be changed depending on box size but I can only put weight on shopify.

So I need some system or app that they can calculate shipping rate automatically.

I've asked support center and one of you guys recommend CCS? CSS? to me but it was like a system on shopify,

So I want to figure out if it is the best option I can do now or is there another better option I can choose. Thank you.