1. The principle: weight or space, whichever costs the carrier more
An aircraft, trailer or container runs out of two things: payload and space. A shipment of pillows fills the hold long before it reaches any weight limit, and a pallet of steel does the opposite. Carriers therefore bill the chargeable weight: the higher of the actual gross weight and the volumetric weight, which expresses occupied space as a weight equivalent.
The calculation takes two steps:
- Volumetric weight (kg) = length × width × height in centimetres ÷ divisor. The divisor states how many cm³ count as one kilogram and depends on the transport mode (next section).
- Chargeable weight = the higher of total actual weight and total volumetric weight.
Note the word total. The comparison is normally decided on the shipment as a whole, not per package: a dense crate can offset a bulky carton in the same shipment. Per-piece values are still worth looking at, because they show which package drives the result. Some tariffs decide per piece or per order position instead, so when the amounts are large, check which basis your contract uses.
2. Divisors and break-even densities by transport mode
Each mode prices space differently, which the divisor reflects. The most useful companion figure is the break-even density: divide total weight by total volume, and if the shipment is denser than the break-even value, actual weight governs; if it is lighter, volumetric weight governs.
| Transport mode | Common convention | 1 m³ counts as | Break-even density |
|---|---|---|---|
| Air freight (IATA convention) | 1:6000 | 167 kg | ≈ 167 kg/m³ |
| Courier and express | 1:5000 | 200 kg | ≈ 200 kg/m³ |
| Road freight (Europe, international) | 1:3000 | 333 kg | ≈ 333 kg/m³ |
| Rail freight | 1:2000 | 500 kg | ≈ 500 kg/m³ |
| Ocean freight LCL | W/M (weight or measure) | 1,000 kg | ≈ 1,000 kg/m³ |
These are market conventions, not binding standards, and carriers apply them with local variations. Some airlines calculate at 1:5000 rather than the IATA convention. European national road tariffs often use their own factors and distinguish stackable from non-stackable cargo. In road freight a second yardstick competes with the volumetric conversion: non-stackable cargo occupies floor space, so loading metres can determine the price instead (covered in Container load planning). In ocean LCL, W/M means the rate is applied per tonne or per cubic metre, whichever is higher. Your freight contract always states the applicable basis; when it deviates, use its divisor rather than the convention.
3. Measure what the carrier will measure
Most disputed volumetric weights come from measuring, not from arithmetic. Carriers measure the packed shipment as handed over, usually with calibrated scales and dimensioning systems at acceptance, and bill from their own values. Measure the same way:
- Packed dimensions, not product dimensions. Measure the greatest extent per axis of the finished package, including the pallet, edge protectors, and any overhang. Cargo that protrudes 5 cm over a 120 cm pallet is 125 cm long for billing purposes.
- Gross weight. Include packaging and pallet tare, not just the net product weight from the packing list.
- Rounding. Common practice in air and courier is to round dimensions to full centimetres and to round the chargeable weight up, often to the next half kilogram. Whether 40.1 kg is billed as 40.5 kg or 41 kg is carrier-specific.
- Consistent units. The divisors above expect centimetres and kilograms. Mixing inches into a centimetre formula produces errors far larger than any rounding rule.
If your own figures and the carrier's regularly disagree, compare one concrete shipment: their measured dimensions are on the invoice or available on request, and the difference is usually overhang, pallet height, or tare that the packing list omitted.
4. Two worked examples
Example 1: light cartons, the divisor decides. Six cartons of 55 × 45 × 40 cm weigh 9 kg each: 54 kg actual weight and 0.594 m³ (density 91 kg/m³). As air freight the volumetric weight is 594,000 cm³ ÷ 6000 = 99 kg, so 99 kg is billed. By courier the same shipment converts at 1:5000 to 118.8 kg. The freight is identical; the billing basis moved by 20 percent because the divisor changed.
Example 2: one pallet across three modes. A pallet of 120 × 80 cm, 125 cm high including the pallet, weighs 460 kg gross. Its volume is 1.2 m³, its density 383 kg/m³:
| Mode | Volumetric weight | Chargeable weight |
|---|---|---|
| Air freight (1:6000) | 200 kg | 460 kg (actual governs) |
| Road international (1:3000) | 400 kg | 460 kg (actual governs) |
| Ocean LCL (W/M) | 1.2 m³ ≡ 1,200 kg | 1.2 revenue units (volume governs) |
The same pallet is weight-rated in the air and on the road, but volume-rated at sea. Whenever you compare modes for a shipment, compare chargeable weights, not scale weights.
5. Doing it with the free Chargeable Weight Calculator
For multi-line shipments the arithmetic is mechanical but error-prone. The free public version of the Spoterix Chargeable Weight Calculator runs in the browser without a signup and applies the logic from this guide:
- Enter or extract the pieces. Type one row per piece type, or paste a packing list or email text, or upload an Excel or PDF file and let AI recognize the lines. Extracted rows stay editable for your review. AI extraction includes one document per day without an account and ten per day with a free Spoterix account.
- Pick the mode, or your contract's divisor. Air, courier, road, rail and ocean LCL presets match the conventions in the table above; the custom mode takes any divisor from a deviating contract. The road mode also distinguishes national and international tariffs, respects a stackable flag, and computes loading metres alongside the volumetric weight.
- Read the decision on the totals. Volume, volumetric and chargeable weight appear per piece and for the whole shipment, with the governing value clearly marked, in metric or imperial units.
Feature scope, privacy notes and frequent questions are collected on the Chargeable Weight Calculator page; all free planning tools are listed on the Tools overview.
6. Chargeable weight in quotes, invoices and Spot Requests
Three habits turn the formula into money saved:
- Specify shipments in billable terms. A Spot Request that states per-piece dimensions, gross weights and stackability lets every supplier compute the same chargeable weight, so quotes differ by price rather than by assumptions. How to structure the request is covered in How to create a Spot Request.
- Recompute before you accept numbers. Check quotes and invoices against your own calculation. When a figure deviates, ask which divisor and which measured dimensions the carrier applied; both are legitimate questions, and the answer usually resolves the difference.
- Act on a governing volumetric weight. When volumetric weight governs by a wide margin, lower packing height, avoid overhang, or reconsider the packaging. Sometimes the better answer is a different mode or equipment; testing whether the freight fits differently is a job for the free Load Calculator.
One limitation applies to all of it: divisors and rounding rules in this guide are widespread conventions, and your contract or the carrier's tariff can define others. For billing, the contract and the carrier's measured values are authoritative; the calculation here tells you what to expect and when to ask questions.