Air Freight Chargeable Weight: Dim Weight Explained

Airlines bill on whichever is higher: what your freight weighs or how much space it takes. The divisor used to convert size into weight is not the same at every carrier, and that difference can move a quote by hundreds of pounds.

The rule in one line

Chargeable weight is the actual gross weight or the dimensional (volume) weight, whichever is higher. Dimensional weight is the volume of the piece divided by a divisor that the carrier sets in its rules or tariff.

For inches and pounds: length × width × height (in) ÷ divisor = dimensional weight (lb). For centimeters and kilograms: L × W × H (cm) ÷ 6,000 = dimensional weight (kg).

The divisors carriers actually use

You will often read that "air freight uses 166." That is true for international shipments under IATA rules and for some US domestic carriers, but not all. Check the carrier's published rules before you quote.

Context	Divisor	Source
International air cargo (IATA rule)	6,000 cm³ per kg (equivalent to 366 in³ per kg or 166 in³ per lb)	IATA TACT Rules 3.9.4, as reproduced in ASEAN air freight training material
Southwest Airlines Cargo, domestic	166 in³ per lb	Southwest Cargo Contract of Carriage
Alaska Air Cargo, domestic	194 in³ per lb (166 for international)	Alaska Air Cargo Rules, Regulations and Charges
Delta Cargo, US domestic rules	194 in³ per lb	Delta Cargo U.S.-Domestic Shipping Rules (published 2012; confirm current version with Delta)

The 6,000 cm³/kg and 166 in³/lb figures are the same standard in different units: 6,000 cm³ is about 366 in³, and 366 ÷ 2.2046 is about 166. A 194 divisor is more generous to the shipper because the same box produces a lower dimensional weight.

Parcel carriers use their own, usually smaller, divisors. Do not mix parcel and air freight numbers in the same quote.

Rounding rules

Rounding is set by the carrier. Examples from published US rules:

Dimensions: Delta's and Alaska's domestic rules drop fractions under half an inch and round half an inch or more up to the next inch. Southwest rounds half an inch or greater up to the next whole number.
Weight: Delta and Alaska round any fraction of a pound up to the next pound.
International (IATA): the ASEAN training material describes rounding dimensions to whole centimeters and weights up to the next half or full kilogram.

Alaska's domestic rules also state that charges are assessed on the greater of actual weight, cubic dimensional weight, or 10 pounds per cubic foot. Read each carrier's rule, because small details like this change the result.

Worked examples

All examples are single pieces with dimensions already rounded to whole inches or centimeters.

Shipment	Actual weight	Volume	Dim weight at 166	Dim weight at 194	Chargeable (166 / 194)
Carton 24 × 18 × 18 in	60 lb	7,776 in³	47 lb	41 lb	60 lb / 60 lb (actual wins)
Pallet 48 × 40 × 50 in	300 lb	96,000 in³	579 lb	495 lb	579 lb / 495 lb
Pallet 48 × 40 × 72 in	400 lb	138,240 in³	833 lb	713 lb	833 lb / 713 lb
Same freight restacked to 48 × 40 × 48 in	400 lb	92,160 in³	556 lb	476 lb	556 lb / 476 lb
Crate 120 × 80 × 100 cm (international)	95 kg	960,000 cm³	160 kg at 6,000 cm³/kg		160 kg

The restacked pallet shows why height matters. Cutting 24 inches of height on a 48 × 40 footprint removed 277 lb of chargeable weight at the 166 divisor, with no change in what was shipped.

Multi-piece shipment example

Take one shipment of three pieces on a carrier using the 166 divisor: two cartons of 20 × 20 × 20 in at 15 lb each, and one crate of 30 × 20 × 15 in at 140 lb.

Piece	Volume	Actual	Dim at 166
Carton 1	8,000 in³	15 lb	48.2 lb
Carton 2	8,000 in³	15 lb	48.2 lb
Crate	9,000 in³	140 lb	54.2 lb
Shipment total	25,000 in³	170 lb	151 lb (rounded up)

Calculated as one shipment, the actual 170 lb is higher than the 151 lb dimensional weight, so 170 lb is billed. If each piece were billed separately at its own higher figure, the total would be 49 + 49 + 140 = 238 lb. That is why it matters whether a carrier rates the whole shipment or each piece, and why light cartons often travel more cheaply when booked together with dense freight. Confirm the method in the carrier's rules before you promise a customer a price.

What to record at pickup

Piece count and type (carton, crate, skid).
Length, width and height of each piece, measured at the widest points including the pallet.
Gross weight from a scale, not the shipper's estimate, when you have one available.
A photo of each piece with a tape measure in frame.

These records settle most disputes when the airline's measured figures differ from the booking.

A quick density check

A divisor is really a density threshold. There are 1,728 cubic inches in a cubic foot, so:

At 166, freight denser than about 10.4 lb per cubic foot (1,728 ÷ 166) is billed on actual weight.
At 194, the break-even is about 8.9 lb per cubic foot.

If you know the weight and the cube of a load, you can tell in seconds whether dimensional weight will apply.

How to cut chargeable weight

Measure before you quote. Airlines re-weigh and re-measure at acceptance, and Southwest's contract reserves the right to do so at tender, intermediate points or destination. A guessed dimension becomes a billing adjustment later.
Lower the stack height. Height is often the cheapest dimension to change. A pallet built tall to save floor space at the shipper costs more in the air.
Right-size cartons. Empty space and oversized void fill are billed as freight.
Remove overhang. Cargo hanging off the pallet edge is measured to its widest point.
Consolidate. Mixing dense and light freight in one shipment can bring the total under the dimensional threshold when the carrier calculates the shipment as a whole. Confirm how your carrier treats multi-piece shipments.
Compare divisors. On domestic moves, a carrier using 194 may cost less for light freight even at a higher rate per pound. Compare total charges, not rates.

Common mistakes

Using 166 for every carrier. Some domestic carriers publish 194. Quote with the right one.
Measuring the carton, not the pallet. The pallet, wrap and any overhang count.
Forgetting minimum charges. Small shipments are often billed at a minimum charge regardless of weight.
Ignoring rounding. On a multi-piece shipment, rounding each dimension up adds up.
Assuming declared value is included. Southwest's domestic contract deems shipments to have a declared value of not more than $0.50 per pound unless a higher value is declared and paid for, and Alaska's rules use the same $0.50 per pound default with a $50 minimum. If a part is worth $10,000, declare it.

If you run the truck leg, measuring and photographing freight at pickup protects you when the airline bill comes back higher than the shipper expected. For pricing the road portion, see setting your rate, and for the paperwork behind the flight, see the air waybill guide.

Questions

Is the air freight dim divisor 166 or 194?

Both are in use. 166 cubic inches per pound matches the IATA international standard of 6,000 cubic centimeters per kilogram and is used domestically by some carriers, such as Southwest Cargo. Others, such as Alaska Air Cargo and Delta's published domestic rules, use 194. Check the carrier's current rules.

How do I calculate chargeable weight in kilograms?

Multiply length, width and height in centimeters, divide by 6,000 to get the volume weight in kilograms, and compare it with the actual gross weight. The higher figure is the chargeable weight, subject to the carrier's rounding rules.

Does dimensional weight apply to heavy freight?

Not usually. If freight is denser than about 10.4 lb per cubic foot at a 166 divisor, or about 8.9 lb per cubic foot at 194, actual weight is higher and is used.

Can the airline change the weight after I tender?

Yes. Carrier contracts reserve the right to re-weigh and re-measure, and charges are corrected to the verified figures.

Air Freight Chargeable Weight: Actual vs Dimensional Weight