What this calculator does
Freight is not sold by the kilogram. It is sold by the chargeable weight — the greater of what the shipment actually weighs and what its volume is deemed to weigh. Enter the outer dimensions of one piece, how many pieces, the weighed gross weight per piece and the divisor from your rate sheet, and this tool returns both figures side by side, tells you which one governs, and by what margin.
The margin is the number that matters. Knowing you are charged 640 kg on a 520 kg shipment tells you that 120 kg of the invoice is air, and air is the one thing on a freight bill you can actually redesign away.
The formula
V_piece = L × W × H (cm³)
W_vol = V_piece ÷ d (kg per piece)
W_act,tot = n × w (kg)
W_vol,tot = n × W_vol (kg)
W_chg = max(W_act,tot , W_vol,tot) (kg)
L, W, H are the outer dimensions of one piece in centimetres — including the pallet, the crate, the shrink wrap and any overhang. n is the number of identical pieces, w the weighed gross weight of one, and d the volumetric divisor in cm³ per kilogram.
The divisor is the only part that is not arithmetic. It is a commercial term in a tariff, not a physical constant, which is why it is an editable field here rather than a hidden constant. The conventional values are 6000 cm³/kg for air freight (the IATA volumetric standard), 5000 for courier and express, 3000 for road groupage, and 1000 for sea LCL.
Every divisor is equivalently a density. Set W_act = W_vol, substitute V_m³ = V_cm³ ÷ 10⁶, and you get the breakeven density:
ρ_be = 1 000 000 ÷ d (kg/m³)
So 6000 cm³/kg is the statement “1 m³ is rated as 166.67 kg”. At 5000 it is 200 kg/m³, at 3000 it is 333 kg/m³, and at 1000 it is 1000 kg/m³ — one cubic metre rated as one tonne, which is exactly the sea freight weight-or-measure (W/M) revenue ton. Compare your shipment’s density with ρ_be and you know the answer before you do any of the rest of the sum.
Why divisors exist at all
An aircraft runs out of volume long before it runs out of lift. A widebody freighter’s lower hold will physically accept far more cubic metres of pillows than the payload limit allows in kilograms of machine parts — but the pillows occupy every position on the aircraft and earn nothing. The divisor exists so that a shipper who consumes the aircraft’s space pays for the space. 6000 cm³/kg was chosen because it sits near the average density of general air cargo, so the carrier is roughly indifferent between a weight-out and a volume-out load.
Sea freight has the same problem in a different shape, and answers it with the revenue ton: the carrier bills whichever is greater, one cubic metre or one tonne, per unit. LCL consolidators quote “per W/M” or “per R/T” for exactly this reason. Road groupage typically uses a harsher ratio (3000 cm³/kg, i.e. 333 kg/m³) or a loading-metre convention, because a trailer’s floor area is the scarce resource and light cargo blocks it just as effectively as heavy cargo.
Reading the result
If volume governs, the shipment is lighter than the breakeven density and you are buying air. The lever is packing, not negotiation: reduce the height of the pack, eliminate void fill, nest the product, or knock down the crate. A 5 cm reduction in stack height on a 120 × 80 cm pallet removes 0.048 m³ per pallet — 8 kg of chargeable weight per pallet on the air basis, before you have spoken to anybody.
If weight governs, the cube is free and the packing is already efficient. Adding protective packaging costs you nothing in freight until you cross back over the breakeven density, which is a genuinely useful thing to know before you decide to skimp on dunnage.
If the two are within a few percent, the tool warns you. This is the dangerous zone: a carrier measuring 121 cm where you measured 119.5 cm can flip the whole shipment onto the other basis. Measure the pack as the carrier will — outermost point to outermost point, wrap included — before you commit to a quote.
Rounding, and why it always goes up
Rounding is a carrier convention, so it is a switch here rather than an assumption. Two conventions dominate:
- Dimensions round up to the next whole centimetre before cubing. 45.3 × 30.7 × 25.2 cm is measured and billed as 46 × 31 × 26 cm — a 5.8% increase in cube from three fractions of a centimetre.
- Chargeable weight rounds up to the next 0.5 kg on air freight. 84.3 kg bills as 84.5 kg.
Neither convention ever rounds down. On a single small parcel the effect is trivial; across a few hundred cartons a month it is not. If you leave rounding off, the tool shows you what the rounded figure would have been, so you can see the gap rather than be surprised by it on the invoice.
Sea LCL is the exception: it is normally rated on cubic metres to three decimal places, or on the revenue ton, usually with a minimum of about 1 m³ per bill of lading. The 0.5 kg step does not apply.
Typical values
| Mode | Conventional divisor | Breakeven density |
|---|---|---|
| Air freight (IATA volumetric) | 6000 cm³/kg | 167 kg/m³ |
| Courier / express | 5000 cm³/kg | 200 kg/m³ |
| Road groupage | 3000 cm³/kg | 333 kg/m³ |
| Sea LCL (W/M revenue ton) | 1000 cm³/kg | 1000 kg/m³ |
These are conventions, not rules. Express carriers have used 4000 and 5000 in different markets and different years; some airlines apply 6000 to general cargo and a tighter figure to named commodities; domestic road tariffs in several countries use a national figure that matches neither 3000 nor 6000. Charter and part-charter air moves are frequently rated on a negotiated divisor or straight on payload. Always take the number from the rate sheet in front of you.
For reference, general air cargo averages roughly 150–200 kg/m³. Palletised consumer goods commonly run 150–250 kg/m³, garments on hangers 60–120 kg/m³, and machinery or metal parts 500–2000 kg/m³.
How to argue a divisor
The divisor is negotiable, and forwarders expect to be asked. What works:
- Bring your density. A forwarder rates a book of business, not a shipment. If your annual profile is consistently 300 kg/m³ you are a weight-out customer subsidising volume-out customers on a 6000 divisor, and that is a legitimate argument for a better all-in rate even if the divisor itself does not move.
- Ask what actually flexes. Divisors are often frozen by the airline’s own tariff. The forwarder’s margin, the fuel and security surcharges, and the break points in the rate scale (+45 / +100 / +300 / +500 / +1000 kg) usually flex more easily than 6000 does. Crossing a break point can beat any divisor argument — if you are at 940 kg chargeable and the +1000 rate is lower per kilo, shipping a declared 1000 kg costs less than shipping 940.
- Bring a redesign, not a complaint. “We can get 12 units per pallet instead of 10 if we knock the crate down” is a conversation about a lower cube. “6000 is unfair” is not.
- Check who measures. Dimensioning scanners at the handling terminal are the arbiter, not your production sheet. If your figures and theirs disagree repeatedly, ask for the scan data — that is a resolvable dispute in a way that the divisor is not.
Worked example
Four crated machine sub-assemblies, each 120 × 80 × 100 cm, each weighing 130 kg gross. Air freight at the standard 6000 cm³/kg divisor, with the usual carrier rounding applied.
Volume of one piece:
120 × 80 × 100 = 960 000 cm³ = 0.96 m³
Total cube is 4 × 0.96 = 3.84 m³. Volumetric weight per piece:
960 000 ÷ 6000 = 160 kg
So the totals are 640 kg volumetric against 520 kg actual (4 × 130). Chargeable weight is the greater: 640 kg. It is already a multiple of 0.5 kg and the dimensions are already whole centimetres, so rounding changes nothing here.
Volume governs, by (640 ÷ 520 − 1) × 100 = 23.1%. You are paying for 120 kg of air. The check confirms it: the shipment’s density is 520 ÷ 3.84 = 135.4 kg/m³, below the 166.7 kg/m³ breakeven for a 6000 divisor.
The lever is the 100 cm height. Take the crate down to 80 cm and the cube falls to 0.768 m³ per piece, the volumetric total to 512 kg — just under the 520 kg actual — and the shipment flips onto the weight basis, saving 128 kg of chargeable weight on the same goods.
FAQ
Which weight goes on the air waybill? Both. The gross weight and the dimensions are declared, and the carrier computes the chargeable weight from them. The rate is applied to the chargeable weight. If the volumetric figure governs, the AWB shows the actual gross weight in the weight box and the higher figure as chargeable — they are not meant to match.
My forwarder used 5000 for an air shipment. Is that wrong? Not necessarily. 5000 cm³/kg is the express and courier convention, and integrator services (the door-to-door express products) apply it to shipments that fly. If it is on a general air freight consolidation, ask — but ask about the rate sheet, not about the physics.
Do I use the pallet dimensions or the goods dimensions? The pallet, always, plus any overhang and the wrap. Whatever the carrier’s dimensioner sees at the terminal is what gets billed, and a 120 × 80 cm pallet with 3 cm of overhang per side measures 126 × 86 cm.
Does chargeable weight apply per piece or per shipment? Per shipment, on the totals. Comparing piece by piece and adding up gives a different — and higher — answer if some pieces are dense and others light, which is not how carriers rate a consolidated consignment. This tool sums both bases first, then takes the greater.
What about sea FCL? It does not apply. A full container is priced per box, so weight and cube only matter against the container’s payload and internal capacity, not against a divisor. Use the container load and CBM calculators for that.
This tool provides indicative figures for quoting and checking. The divisor, rounding convention and minimum charges that actually apply are those in your carrier’s or forwarder’s tariff — confirm them against the rate sheet before you commit to a price.