Sea, rail or air — and why the answer is often all three
The cheapest freight decision is rarely one mode for the whole order. It is the cheapest mode that still arrives in time.
The trade-off
Roughly, and it varies by lane, season and carrier:
| Mode | Typical door to door | Relative cost per kg |
|---|---|---|
| Sea | Around three months | Cheapest by a wide margin |
| Rail | Several weeks | Between the two |
| Air | Days | Several times sea |
Treat these as shapes, not quotes. What matters is the ratio: air is not slightly more expensive than sea, it is a different order of magnitude, which is why an avoidable air shipment can wipe out the margin on the goods it carries.
Why one mode for the whole order is usually wrong
Suppose you have 40 days of stock and sea freight takes 100 days. Send everything by sea and you are empty for 60 days. Send everything by air and it arrives in time, at several times the cost, including the units you would not have needed for months.
The cheaper answer is a split: the bulk goes by sea because most of it is not needed until later, and a small quantity comes by air or rail purely to bridge the gap until the sea shipment lands. You pay premium freight only for the units that genuinely cannot wait — often a small fraction of the order.
Done by hand this is tedious, because the bridge quantity depends on the sales rate, the gap between the modes' lead times, and whatever is already in transit. Done automatically it is just arithmetic, per product, every day.
The cost of deciding late
Every day you delay past the sea-freight deadline, the boat lands one day further past the point your stock runs out — so the bridge you need by air gets bigger. The freight bill for lateness grows quietly, and it is almost never attributed to the decision that caused it.
What to track
- Realistic door-to-door lead time per mode, including production and customs, not just sailing time.
- A safety buffer per mode, because delays are normal.
- Weight per unit — freight is priced per kilo, so without weights you cannot compare modes at all.
- Your actual freight rate per kilo per mode, taken from a real invoice rather than a list price.
- Landed cost per unit: goods plus freight plus duties, which is the only number that tells you the true margin.
This is the part of purchasing that general inventory tools do not touch, and it is what Restocio was built around.
Common questions
Is it cheaper to ship everything by sea?
Per kilo, yes. But if the shelf empties before the ship arrives, the lost sales and the emergency air freight that follows usually cost more than the saving. The cheapest total outcome is normally sea for the bulk plus a small air or rail bridge.
What is landed cost?
What one unit actually costs you on your shelf: the price paid to the supplier plus its share of freight, plus duties and any other import costs. Margin calculated on the supplier price alone overstates profit, sometimes badly.
Related guides
- Looking for a Stocky alternative?
- Export your Stocky data before 31 August 2026
- Stock replenishment, end to end
Restocio plans purchasing for Shopify stores that import. It works out what to order, how much, and whether it should travel by sea, rail or air — so you pay air freight only for the units that genuinely cannot wait.