I used to be against shipping calculators because I thought the agents had every reason to give you cheap estimates to win comparisons and later say the parcel was heavier to get more money.
My opinion on shipping calculators changed after I measured a parcel myself and compared it to what the agent measured. It turns out the agents (in this case Wegobuy) work really precise and honest. Here's the video where I recorded my experience: YouTube Link
The price is decided by 3 factors:
- Weight: As I said this one is surprisingly reliable.
- Price per weight unit: easy to check. This is the last thing the agents would cheat on.
- Exchange rate: There's always a risk of it changing between the order and shipping, but that could be in both directions.
So with this knowledge shipping calculators seem like a helpful tool.