Air freight vs sea freight: how to choose per shipment

• Sea: cheapest per kilogram for most cargo, weeks in transit, priced per container or per CBM, needs an ISF into the US.
• Air: days in transit, priced per chargeable kilogram, strict rules for batteries and other dangerous goods, no ISF.

Air freight charges the greater of the actual weight and the volumetric weight. IATA’s general rule is the volume in cubic centimetres divided by 6,000. A carton of 60 × 40 × 40 cm weighs 16 kg by volume, so if the real weight is 8 kg you pay for 16. Bulky, light goods lose most of the speed advantage to price; small, dense goods do not.

Sea freight in a shared container is priced by weight or measure, and a full container per box, so light goods suffer less. Check your figures with the DDP calculator, which shows the chargeable weight.

• Sea: replenishment planned weeks ahead, heavy or bulky goods, full containers.
• Air: a product launch, a reorder that came too late, high-value goods where days on the water cost more than the freight, samples.
• Many sellers split one order: a small air shipment to cover the gap, the rest by sea.

Lithium batteries are the most common snag. Under IATA rules for 2026, lithium-ion batteries shipped on their own travel on cargo aircraft only, at no more than 30% state of charge, and from 1 January 2026 the same 30% limit applies to many batteries packed with equipment. Lithium metal batteries shipped on their own are forbidden on passenger aircraft. Some airlines refuse them entirely. Tell the carrier about any battery before it prices.

An Importer Security Filing is required only for goods arriving in the US by vessel, so sea freight needs one and air does not; air cargo data is sent under separate advance rules by the airline and forwarder. See ISF filing. The Harbor Maintenance Fee applies to sea cargo, not air. See landed cost.

1. Work out the chargeable weight by air and the CBM by sea.
2. Ask what each day of stock-out would cost you in lost sales.
3. Price both modes for the same cargo.
4. Choose air when the freight difference is smaller than the cost of waiting.

The shipment form asks for the mode: sea standard, sea express, air or land. Post the same cargo by sea and by air, and the bids show what the faster transit costs on your lane. The form’s guide price shows past winning bids per mode once there are enough.