The per-kg number is an output, not an input. It falls out of the dimensions, the lane, the week you are flying and what is in the box. Anyone who gives you a firm per-kg figure before asking for those is guessing, and the guess will be revised once the cargo is measured.
That is not evasion. Once you understand the structure you can read a quote properly, challenge the parts that are wrong, and occasionally pay less by shipping more. This page explains the components without inventing rates, because a rate quoted in an article is out of date before you read it.
You are not charged for what your cargo weighs
Aircraft run out of space before they run out of lift. So air freight is charged on chargeable weight, which is the greater of the actual gross weight and the volumetric weight.
For air cargo the standard volumetric divisor is 6000. Take the volume of each piece in cubic centimetres and divide by 6000 to get a weight in kilogrammes:
Volumetric weight (kg) = length × width × height in cm ÷ 6000
A worked example. Six cartons, each 60 × 40 × 40 cm, gross 11 kg apiece.
- Volume per carton: 60 × 40 × 40 = 96,000 cm³. Six cartons = 576,000 cm³.
- Volumetric weight: 576,000 ÷ 6000 = 96 kg.
- Actual gross weight: 6 × 11 = 66 kg.
- Chargeable weight: the greater of the two, so 96 kg.
You pay for 96 kg and hand over 66 kg. Two cautions. Express and courier operators commonly use a divisor of 5000, which produces a higher chargeable weight for the same box. And chargeable weight is rounded up, usually to the next half kilogramme — confirm the rule with whoever is quoting. The same arithmetic in cubic metres is what our CBM calculator does for sea cargo.
Rate breaks, and why a heavier shipment can cost less
Air freight rates step down as weight increases. The bands you will see on a quote are conventionally written as:
| Band | Applies to chargeable weight |
|---|---|
| M | Minimum charge — a flat amount for very small consignments, below the point where a per-kg rate makes sense |
| N or -45 | Normal rate, under 45 kg |
| +45 | 45 kg and above |
| +100 | 100 kg and above |
| +300 | 300 kg and above |
| +500 | 500 kg and above |
| +1000 | 1,000 kg and above |
Not every carrier publishes every band on every lane. Some stop at +500; some add breaks at +250 or +2000. Ask which apply to your lane rather than assuming the full ladder exists.
Because each band is a lower per-kg rate applied to the whole shipment, there is a stretch just below each break where declaring the higher weight is cheaper. Take the 96 kg shipment above, and two illustrative rates — these are not quotes, they exist only to show the arithmetic. Say the +45 rate is 4.20 per kg and the +100 rate is 3.50 per kg.
- Charged as 96 kg at the +45 rate: 96 × 4.20 = 403.20
- Charged as 100 kg at the +100 rate: 100 × 3.50 = 350.00
The heavier declaration is cheaper by 53.20, for the same cargo. This is standard practice, not a trick, and it is usually called shipping at the higher weight break. The break-even point is the higher band’s threshold weight multiplied by its rate, divided by the lower band’s rate: 350.00 ÷ 4.20 = 83.33 kg. Anything above roughly 83.3 kg chargeable is cheaper declared as 100 kg.
A forwarder quoting you should already have done this. If your quote sits at 92 kg on a +45 rate, ask why it is not charged at 100.
What else is on the invoice
The per-kg rate is only the airline’s carriage. Around it sit charges that add materially to the total, particularly on light shipments where the fixed items dominate.
| Component | How it is charged | Notes |
|---|---|---|
| Air freight rate | Per chargeable kg, by rate break | The headline number. Varies by lane, carrier and week. |
| Fuel surcharge | Per chargeable kg | Set by the carrier, revised periodically, tracks fuel prices. On some lanes it is a significant fraction of the freight itself. |
| Security surcharge | Per chargeable kg | Smaller than fuel, but still per kg rather than flat. |
| Terminal handling at origin | Per kg, usually with a minimum | Charged by the airline or the cargo terminal operator at the departure airport. |
| X-ray or screening | Per kg or per piece, with a minimum | Cargo that cannot be screened by X-ray may need alternative screening, which costs more and takes longer. |
| Air waybill fee | Flat, per AWB | Small, but it does not scale down for a small shipment. |
| Customs clearance | Flat, per shipping bill or bill of entry | Your broker’s agency fee, separate from disbursements. See customs clearance. |
| Pickup and trucking | By distance and vehicle | Ahmedabad to a Mumbai or Delhi gateway is a real cost line, not a rounding error. |
| Destination charges | Varies | Import handling, delivery order and clearance at the other end. Under most Incoterms these are not yours, but confirm rather than assume. |
On a 45 kg shipment the fixed items — AWB fee, clearance, screening minimum, pickup — can rival the freight. On a 1,000 kg shipment they are noise. That is why per-kg all-in costs look so different at different weights, and why comparing two quotes only on the freight line tells you very little.
What actually moves the rate
- Lane. Rates are directional and reflect the balance of trade on the route. The same pair of airports can be priced very differently in each direction. Our lanes pages set out the routes we work most.
- Season. Two peaks matter for Indian exporters. The run-up to Christmas, roughly from September into November, tightens westbound capacity. And the weeks before Chinese New Year, whose date moves each year between late January and mid-February, tighten space across Asia as factories push to ship before the shutdown. Rates rise in both windows and space is the real constraint, not price.
- Direct versus transhipment. A direct flight costs more and arrives sooner. A routing through a hub adds a day or two and a handling point where cargo can be offloaded if the connecting flight is full. On urgent cargo the cheaper routing is often false economy.
- Capacity type. Most air cargo travels in the belly of passenger aircraft. When passenger schedules thin out on a route, belly capacity goes with them and rates move regardless of demand.
- Commodity. Dangerous goods cost more — declaration, packing to the applicable regulations, restricted acceptance, and some carriers refuse certain classes outright. Pharmaceutical cargo needing temperature control costs more again, through active containers or validated passive packaging. General cargo is the cheapest thing in the hold.
- Density. Cargo that fills the hold before it reaches the weight limit is priced accordingly. This is the same problem as its sea equivalent, in reverse.
What to send us for a real number
A quote request with these seven items can be answered accurately. One without them cannot.
- Origin and destination — city and airport, not just country
- Number of pieces, and the length, width and height of each in centimetres
- Gross weight of each piece in kilogrammes
- Whether the cargo is palletised, and the pallet dimensions and height if so
- Commodity description, and the HS code if you have it
- Whether it is dangerous goods, temperature-controlled or perishable
- Ready date, required arrival date, and the Incoterm
If the cargo is not yet packed, send estimated dimensions and say so. A quote against stated assumptions is far more useful than a number with no basis. More on our air freight page, and the terms above are defined in the glossary.
Frequently asked questions
Why does the same shipment get three different per-kg rates from three forwarders?
Usually because they are not quoting the same thing. One excludes origin terminal handling, another includes clearance, a third routes through a different hub with a longer transit. Ask all three for the same breakdown — freight, fuel, security, handling, screening, AWB, clearance, pickup — and comparison becomes possible. Differences in the airline’s own rate are usually smaller than differences in what has been left out.
Is air freight always charged on volumetric weight?
No. It is charged on whichever is greater, actual or volumetric. Dense cargo — machined parts, hardware, chemicals in drums — is normally charged on actual weight. Light bulky cargo is charged on volume. Roughly, cargo lighter than about 167 kg per cubic metre will be charged on volume at the 6000 divisor, because one cubic metre of volume equals 1,000,000 cm³ divided by 6000, which is about 166.7 kg.
Can I reduce the chargeable weight by repacking?
Often, yes, and it is the cheapest saving available. Removing void space, reducing carton height, and choosing carton sizes that stack without gaps all reduce volumetric weight directly. It is worth doing the arithmetic before you order packaging rather than after the cargo is at the airport.
How far in advance should I book during peak season?
It varies by lane and by year, so treat any single figure with suspicion. The practical rule is that in the Christmas and Chinese New Year windows, confirming space matters more than negotiating the rate, and a booking not confirmed against a specific flight is not really a booking. Ask earlier than feels necessary and you keep the option of a cheaper routing.