Choosing Between Air and Sea for Machined Parts

By CNC Machining Vietnam·Published September 21, 2026·Editorial standards

For most goods the air versus sea decision is a straight trade between money and time. For machined parts it is less obvious, because metal parts are dense, often valuable per kilogram and frequently urgent. Those three properties pull the answer in different directions.

Why density changes the arithmetic

Air freight charges on chargeable weight, which is the greater of actual weight and volumetric weight. The common air conversion divides volume in cubic centimetres by 6000, which is about 167 kg per cubic metre.

Sea freight in less than container load quantities charges on w/m, the greater of the weight in tonnes and the volume in cubic metres, which works out at 1000 kg per cubic metre.

Machined metal parts sit far above both thresholds. A crate of steel or aluminium components is dense enough that you pay on actual weight in either mode.

What this means in practice:

• Air: you pay full weight, with no benefit from compact packing. Air is expensive for machined parts specifically because they are heavy for their size.
• Sea LCL: you pay on weight too, but at a far lower rate. The volume you save by packing tightly buys you nothing, so there is no point paying for clever packaging.

This is the opposite of a shipment of plastic housings or foam, where volume dominates and packing efficiency is worth real money.

The decision in four questions

1. What does a day of delay cost you?

If a line stops, the answer is usually far more than the freight difference and the decision is made. If it is inventory arriving three weeks earlier than needed, sea wins easily. Put a number on it before comparing quotes, because without one every urgent shipment feels urgent.

2. How heavy is the consignment?

Small and light consignments, meaning a few cartons, are often cheaper by express courier than by any other route once handling charges are counted. As weight rises, air freight through a forwarder becomes better value than express, and above a few hundred kilograms the gap to sea widens quickly.

3. Is it a one off or a repeating order?

A first order with an unproven shop benefits from arriving quickly, because everything you learn from it is delayed by the transit. A repeating monthly order should be on sea with a pipeline, where one shipment is in transit while the previous one is in use.

4. What is the value density?

A crate of precision parts can be worth more than a container of most goods. High value per kilogram justifies the air premium more easily, and it changes your insurance decision in both modes.

How the modes compare

	Express courier	Air freight	Sea LCL	Sea FCL
Typical use	A few cartons	Hundreds of kilograms	Part load, palletised	Full container
Charged on	Chargeable weight	Chargeable weight	Greater of tonne or cubic metre	Per container
Customs	Carrier handles it	You or your broker	You or your broker	You or your broker
Door to door	Yes	No, airport to airport	No, port to port	No, port to port
Relative cost per kg	Highest	High	Low	Lowest at volume
Handling touches	Few	Several	Many	Fewest

That last row matters more for machined parts than for most cargo. Every time an LCL consignment is deconsolidated it is handled, and handling is where finished surfaces get marked. See the guide to export packing for what to specify.

Transit is not the same as lead time

The number a forwarder quotes is port to port or airport to airport. Your actual door to door time includes:

• Collection and delivery to the port or airport
• Export clearance
• Waiting for a sailing or a flight with space
• The transit itself
• Arrival handling and deconsolidation
• Import clearance, which depends on your documents being right
• Inland delivery to you

The steps either side of the transit are usually where the surprises are, and they are roughly the same whichever mode you pick. A sea shipment quoted at three weeks port to port is not a three week shipment. Build the whole chain when you plan, using the same approach as the lead time breakdown.

The split shipment, which almost nobody asks for

If a shop is making 500 pieces and you need 40 of them urgently, ask for a split: 40 by air as soon as they are inspected, the remaining 460 by sea.

You pay the air premium on eight percent of the order instead of all of it, your line keeps running and you get an early look at real production parts while there is still time to correct something. Most shops will do this without complaint if you ask before production starts. Asking afterwards means repacking, which they will charge for.

Insurance, briefly

None of the common Incoterms for this trade obliges anyone to insure the goods. Under EXW, FOB, DAP and DDP alike, cover is optional and frequently absent.

Machined parts are a poor thing to self insure. The replacement cost is not the invoice value, it is the invoice value plus the entire lead time again. Buy cover, and buy it on the landed value rather than the ex works value.

A workable default

For a first order of a few hundred parts, air freight or express, because the speed buys you information.

For a repeating order, sea, with enough stock in the pipeline that a delayed sailing does not stop anything.

For an emergency, express on a split shipment rather than the whole order, every time.

When you want quotes that make this decision concrete, put the destination and your deadline on the RFQ. Send the drawing here and the shops quoting will price the shipping term you ask for.

Frequently asked questions

Keep reading

• Certificates of Origin for Parts Made in Vietnam
• Packing Machined Parts So They Arrive as They Left