Compare on cost per unit, not per kilo
Air freight is priced on weight, sea freight on volume. The comparison only makes sense once both are expressed as a cost per saleable unit, which is why a dense, expensive product often flies economically while a bulky, cheap one never does.
Put a number on the time
Sea is typically four to eight weeks door to door depending on the corridor; air is days. The question is what those weeks cost you: capital locked in transit, a missed season, or an empty shelf that a competitor fills.
The hybrid that usually wins
Experienced importers split the shipment: a small first batch by air to start selling, test the market and catch defects early, with the bulk following by sea. You get speed where it matters and cost where it does not.
Rail and courier, the forgotten options
For some destinations, rail sits usefully between sea and air on both cost and time. And for genuinely small consignments, an express courier with duties prepaid can beat a formal freight booking once you count clearance fees and your own hours.