Air cargo is billed on chargeable weight — the higher of actual weight and volumetric weight. Volumetric is length × width × height in cm ÷ 5,000. A 60 × 40 × 40 cm box is 19.2 kg volumetric, so a 9 kg box of light goods gets billed at 19.2 kg.
This is the single most common surprise on an air freight quote: you weigh your box at 9kg, and the price comes back as though it weighs 19kg. Nothing has gone wrong. You have met volumetric weight.
Why airlines charge for space, not just weight
An aircraft runs out of room long before it runs out of lifting power. A box of pillows and a box of tinned tomatoes might both weigh 10kg, but the pillows occupy five times the space — space that cannot be sold to anyone else. So the industry prices on whichever is greater: what the shipment weighs, or what it takes up.
The sum
Measure the box in centimetres, multiply the three dimensions, divide by 5,000:
| Box size (cm) | Volumetric weight | If it actually weighs… | You are billed |
|---|---|---|---|
| 40 × 30 × 30 | 7.2 kg | 10 kg | 10 kg (actual wins) |
| 50 × 40 × 40 | 16 kg | 12 kg | 16 kg (volumetric wins) |
| 60 × 40 × 40 | 19.2 kg | 9 kg | 19.2 kg (volumetric wins) |
| 60 × 50 × 50 | 30 kg | 28 kg | 30 kg (volumetric wins) |
Whichever number is higher is your chargeable weight — the figure the rate per kilo is applied to. Our cost estimator does all of this for you and shows the air and sea prices side by side.
The divisor matters more than people realise
Most operators on this route divide by 5,000. Some couriers divide by 4,000 — and because a smaller divisor produces a bigger number, the identical box costs more with them. On our 60 × 40 × 40 example that is 19.2kg against 24kg: the same box, five kilos of difference, purely from the formula.
How to pay less
- Use a smaller box. The most effective change available. An oversized box charges you for air.
- Fill it completely. You are paying for the whole box whether it is full or not.
- Vacuum-bag soft items. Duvets, coats and bedding compress dramatically, and compression is money back.
- Remove retail packaging. Boxes inside boxes are pure volumetric cost.
- Send bulky things by sea. Volumetric weight barely bites on sea freight. If it is light and enormous, it belongs in a barrel.
The minimums nobody mentions
Below a certain size you pay a floor price regardless: 10 kg by air to Lagos, 25 kg to other states, and 50 kg by sea on this route. A 3kg parcel to Lagos is billed as 10 kg, which is worth knowing before you send several small parcels separately — combining them into one shipment means paying one minimum and one handling fee instead of several.
Air rates start from £4.80/kg to Lagos (collected from our Lagos office) with a 10 kg minimum. Work out your chargeable weight with our estimator, or send us the dimensions and we will do it.
Common questions
What is volumetric weight?
It is a weight worked out from a box's size rather than the scales: length × width × height in centimetres, divided by 5,000. Air cargo is billed on whichever is higher — the volumetric weight or the actual weight — because bulky boxes take space the aircraft cannot sell twice.
How do I calculate volumetric weight?
Multiply length × width × height in centimetres, then divide by 5,000. A 60 × 40 × 40 cm box gives 96,000 ÷ 5,000 = 19.2 kg volumetric. If the box actually weighs 9 kg, you are billed on 19.2 kg.
Why is my parcel more expensive than its weight suggests?
Almost always volumetric weight. Light, bulky contents — duvets, nappies, empty containers, cushions — take up far more space than their scale weight implies, so the volumetric figure becomes the billed figure.
Does volumetric weight apply to sea freight?
Not in the same way. Sea is usually charged per kilo or per cubic metre with a 30 kg minimum, so bulky-but-light loads are far cheaper by sea than by air. That is exactly why barrels go by sea.
Some couriers divide by 4,000 — what does that mean?
A smaller divisor produces a bigger volumetric weight, so the same box costs more. Always ask which divisor a quote used. We use 5,000 and tell you the chargeable weight up front, so the number you agree is the number you pay.
How can I reduce my volumetric weight?
Use a smaller box and fill it completely. Vacuum-bag soft items, remove packaging air, and never send a half-empty box — you are paying for the space either way. Squaring off an oversized box is often the single biggest saving available.