How air and sea freight are priced
I have seen buyers default to sea freight for a 20 kg prototype shipment because they assumed it was always cheaper. It was not. Air and sea use completely different pricing models, and the break-even point depends on weight, volume, urgency, and how badly you need the parts.
Air freight is priced by chargeable weight, which is the greater of actual weight and volumetric weight (length x width x height in cm divided by a volumetric divisor, typically 6000 for standard air). Dense metal parts hit actual weight; bulky lightweight packaging hits volumetric. Express air (courier door-to-door) costs more per kilogram than standard airport-to-airport air freight but includes pickup, clearance, and delivery.
Sea freight is priced by container (FCL, full container load) or by volume/weight for less-than-container loads (LCL, typically charged per cubic meter or per 1,000 kg, whichever is greater). For a small batch of CNC machined parts, LCL is the realistic sea option unless you are shipping enough to fill a 20-foot or 40-foot container.
Real transit times from China
Transit time depends on origin, destination, routing, and time of year. These are industry-standard ranges for major routes from South China (Shenzhen/Guangzhou/Hong Kong), but actual times vary by carrier, routing, customs inspection, and season.
| Mode | Typical transit time | Notes |
|---|---|---|
| Express air (courier) | 3-5 days door-to-door | DHL/FedEx/UPS; includes clearance; fastest but most expensive per kg |
| Standard air freight | 5-10 days airport-to-airport | Add 1-3 days on each end for pickup, customs, and delivery |
| LCL sea freight | 25-40 days port-to-port | Add 5-10 days consolidation and deconsolidation at both ends |
| FCL sea freight | 20-35 days port-to-port | Direct routing faster than transshipment; add trucking time to and from ports |
During peak season (typically August through October before Western holidays, and before Chinese New Year in January or February), add 1-2 weeks across all modes due to capacity constraints and port congestion. These are general ranges; actual transit time varies by route, carrier, and external factors.
When air freight makes sense
Air freight is not always the wrong choice for metal parts. I have had production emergencies where a 30 kg batch of critical components was air-freighted to avoid a line-down situation, and the freight cost was trivial compared to the daily downtime cost.
- Prototype and first-article batches under 50-100 kg where lead time matters more than per-unit freight
- Emergency replacements or line-down situations where 25-40 days of ocean transit costs more than the air premium
- High-value, low-weight parts where freight is a small percentage of total shipment value
- Shipments with firm deadline pressure such as trade shows, product launches, or customer penalty clauses
When sea freight is the right call
For production quantities, sea freight is almost always the better economic choice. The cost per unit drops dramatically with volume, and if you plan ahead with buffer stock, the transit time becomes a scheduling issue rather than a crisis.
- Production batches exceeding roughly 100-200 kg or more than a couple of cubic meters where air freight cost would exceed part value savings
- Recurring orders where you can build a 4-6 week buffer into inventory planning
- Low-margin parts where freight is a significant percentage of landed cost
- FCL shipments where per-unit freight cost drops substantially versus LCL
A practical decision framework
There is no single weight threshold that works for every route or product, but the decision can be framed around three questions. First: what is the cost of delay? If your production line stops without these parts, air freight pays for itself quickly. Second: what percentage of total order value does freight represent? If air freight is a small fraction of part value and saves three weeks, it is often worth it; if it approaches or exceeds part value, plan for sea. Third: can you plan ahead? If the order is on a forecast rather than a hot need, sea freight with buffer stock is almost always cheaper.
Frequently Asked Questions
Is express air (DHL/FedEx) the same as air freight?
No. Express is door-to-door courier service with integrated clearance, fastest but highest cost per kg. Standard air freight is airport-to-airport; you or your forwarder arrange pickup, clearance, and last-mile separately, which is cheaper per kg but adds handling steps.
How much cheaper is sea vs air?
The gap varies widely by route, fuel prices, and season, but sea freight per unit weight is typically an order of magnitude lower than air. For large shipments the difference is even greater. Request quotes for both modes on your specific shipment rather than relying on rules of thumb.
Should heavy parts always go by sea?
Not always. A 50 kg urgent replacement part still makes sense on express air if it prevents a production stoppage. The mode decision depends on urgency and downtime cost, not just weight.
What about rail freight from China to Europe?
Rail is a middle option: faster than sea (roughly 14-20 days) and cheaper than air, but with limited destinations and less frequent departures. Worth considering for European buyers with moderate urgency.
Do I need cargo insurance?
Yes, for both modes. Carrier liability is limited by international conventions and rarely covers the full commercial value. Insure for CIF (cost plus insurance plus freight) value plus 10 percent.