The conclusion in one line
The lane that looks cheapest in a comparison table is the one with the most conditions attached, and those conditions are usually about branded goods and tracking. That is not a reason to avoid it. It is a reason to read the conditions before you pick a lane, rather than after a parcel is refused at handover.
Nobody here can hand you a per-kilogram price. This site does not publish a fee figure it has not read on the platform itself, and the shipping weight estimate is built around that limit: you enter the parcel, it returns a range from figures you supply, and it states plainly that the result is an estimate rather than a quote.
Five numbers that decide it
One, billing weight. That is the greater of actual weight and volumetric weight, and volumetric weight typically comes from length times width times height divided by a divisor. A light parcel of shoes is not billed as a light parcel, because the divisor is a convention and the boxes are large.
Two, destination region. The same parcel to the United States, the United Kingdom, the European Union, Canada or Australia can land in different bands. Three, line type: the cheapest lane is usually the slowest, and it is also the one most likely to exclude branded goods or skip tracking.
Four, branded goods. A parcel holding branded items is filtered into a narrower set of lanes than the same parcel without them, and that filter often matters more than weight. Five, season. Peak surcharges arrive on a schedule that has nothing to do with your order date, and a quote taken in a quiet month does not hold in a busy one.
Three questions people ask
Which lane is fastest? The one with the shortest stated transit window, which is almost never the cheapest. Transit windows are quoted by the lane rather than by your parcel, and clearance sits underneath all of them. Two parcels on the same lane can land days apart without anything having gone wrong.
Can I switch lanes after paying? Once a parcel is handed to a line it usually stays there, though some services allow an upgrade before dispatch. The platform ledger records what this site could verify about each platform, and it marks fees, storage days and payment methods as unverified rather than filling them in.
Why will nobody publish a rate? Because rates change without notice and a stale figure is worse than none. Run your own numbers through the shipping weight estimate with the current rate for your lane, and treat the output as a way to compare lanes, not as the amount you will be charged.