Air Freight Rate Weight Breaks: Minimum, -45, +45 and +100

A forwarder's invoice arrives for four cartons flown from Chennai: 82 kg at the +45 rate. The shipper's own packing list says 59.2 kg gross. Somebody in accounts payable approves it because the rate per kilogram matches the contract. Nobody asks why the weight is higher than the scale ticket, or whether 82 kg on the +45 rate should have been billed as 100 kg on the cheaper +100 rate.

Both questions have exact answers. Air cargo is priced on a published ladder of weight breaks, and the tariff rules say how to measure the consignment, how to round it and when a heavier notional weight produces a lower charge. A buyer who can rerun that arithmetic catches overbilling on each invoice line, and can negotiate a rate card that matches the weights the business actually ships.

• What this guide explains: the minimum charge, the -45 normal rate, the +45, +100 and higher quantity rates, chargeable weight, rounding and the break-point formula.
• What it works through: a US export rated in USD from inch measurements, an Indian export rated in INR that crosses the 100 kg break, the air waybill rate line, an audit trace and a checklist for negotiating the card.

What M, -45, +45 and +100 mean on an airline rate sheet

An airport-to-airport general cargo rate card is a ladder: one flat minimum charge per consignment, then a per-kilogram rate that falls as the weight band rises. The column headings are shorthand for those bands, and each one maps to a rate class code that later appears on the air waybill.

The minimum charge, rate class M, is the least an airline will accept for any consignment on that lane. The normal rate, rate class N, is the per-kilogram price for consignments under 45 kg, which is why sales sheets label it "-45". Quantity rates, rate class Q, start at 45 kg ("+45") and continue at heavier breaks such as +100, +300, +500 and +1000. Each quantity rate applies from its stated minimum weight up to the next break.

The ASEAN training material that reproduces the IATA TACT rules notes that the normal rate covers consignments under 45 kg in most countries, but up to 100 kg in some, because the +45 break has been withdrawn there. Read the card in front of you: a missing +45 column changes every break point below 100 kg.

Air freight weight breaks follow the IATA TACT rate structure: a per-consignment minimum charge (rate class M), a normal rate below 45 kg (rate class N) and quantity rates (rate class Q) from 45, 100, 300, 500 and 1,000 kg, each priced per kilogram of chargeable weight and recorded on the air waybill rate line.

Chargeable weight comes first: gross, volume and the 6,000 divisor

No weight break can be chosen until chargeable weight is fixed. Chargeable weight is the higher of the consignment's gross weight and its volume weight, and IATA's general rule converts volume to weight by dividing cubic centimetres by 6,000.

Gross weight includes everything that flies: cartons, pallets, strapping, bracing and corner boards. Volume weight uses the greatest length, greatest width and greatest height of each piece, so a carton with a protruding handle is measured to the end of the handle. TACT Rule 3.9.4, as reproduced in the ASEAN material, also gives 366 cubic inches per kilogram and 166 cubic inches per pound as the equivalents for inch measurements.

• Metric volume weight: length x width x height in cm, multiplied by the piece count, divided by 6,000, giving kilograms.
• Inches to kilograms: length x width x height in inches, multiplied by the piece count, divided by 366.
• Inches to pounds: the same cubic inches divided by 166, used where a US origin rates per pound.
• Three decimals before rounding: the volume weight is calculated to three decimal places and only then rounded.

Light, bulky goods such as apparel, lampshades or foam-packed electronics are usually volume-rated. Dense goods such as fasteners, castings or printed paper are usually gross-rated. Our PTL chargeable weight guide covers the same higher-of logic for Indian part-truckload road freight, where the conversion factor is set by each carrier's contract. Air differs in two ways: the divisor is an industry convention, and the rate ladder adds break points that road slabs rarely have. Parcel carriers use other divisors, which our guide to DIM divisors compares.

Rounding dimensions and kilograms the way TACT rules expect

Two rounding rules sit between the tape measure and the invoice, and most billing disputes in small consignments trace back to one of them. Dimensions round to the nearest whole unit; weights round upward in half-kilogram steps.

• Centimetre fractions: 0.5 cm or more rounds up to the next whole centimetre; less than 0.5 cm rounds down. A 48.5 cm side becomes 49 cm, and 40.2 cm becomes 40 cm.
• Inch fractions: half an inch or more rounds up; less than half rounds down. A 20 1/4 in side becomes 20 in.
• Kilogram fractions: 0.1 to 0.4 kg rounds up to the next half kilogram, more than 0.5 kg rounds up to the next whole kilogram, and exactly 0.5 kg stays as it is.
• Pound fractions: any fraction of a pound rounds up to the next whole pound.
• Whole consignment: add the cubic volume of all pieces first, divide once, then round. Rounding each piece and adding the results overstates the weight.

The last rule matters more than it looks. In the Indian example later in this guide, four identical cartons each come to 20.253 kg of volume weight. Rounded piece by piece, that is 20.5 kg x 4 = 82.0 kg. Divided once on the combined volume, it is 81.013 kg, rounded to 81.5 kg. The half kilogram is small; the habit of rounding piece by piece across thousands of air waybills is not.

Break-point math: when billing at the next break costs less

A consignment just below a break can cost more at its own band than at the next break's minimum weight. The tariff rules allow the lower charge: rate the consignment at the higher break weight and the lower rate whenever that product is smaller.

The ASEAN deck shows the rule with a 995 kg consignment: 995 kg at a 500 kg break rate cost more than 1,000 kg at the 1,000 kg break rate, so the charge was raised to a chargeable weight of 1,000 kg. The point where the two charges meet is the break point. Above it, every consignment in the lower band should be billed at the higher break.

Break point (kg) = (W_next x R_next) / R_current
  W_next    = minimum weight of the next break, kg (e.g. 100)
  R_next    = rate per kg at the next break
  R_current = rate per kg in the consignment's own band
Round the result up to the next 0.5 kg.

Minimum-charge threshold (kg) = M / R_N
  M   = minimum charge per consignment
  R_N = normal (-45) rate per kg
At or below the threshold, bill M.

Rating rule for chargeable weight CW in band b:
  charge = min( CW x R_b , W_(b+1) x R_(b+1) , W_(b+2) x R_(b+2), and every higher break )
  charge = max( charge , M )
  if the winning term is a higher break, record that break
  weight as the chargeable weight on the AWB

Check every higher break, not only the next one. On a card where the +300 rate is unusually low, a 230 kg consignment can be cheaper at 300 kg than at either its own band or the +100 alternative. A rating engine that compares only adjacent bands will miss it.

Break-point math for air freight divides the next break's minimum weight times its rate by the current band rate; under the TACT lower-charge-at-higher-weight method, a +45 rate of $4.90 and a +100 rate of $3.70 give a 76.0 kg break point, so consignments from 76.0 to 99.5 kg bill as 100 kg.

Worked US export: inch measurements and a USD rate card

A US exporter's rate card from a forwarder, in US dollars per kilogram, produces six break points. The card below is illustrative; the arithmetic is what a buyer should rebuild for each lane and each card revision.

Check one line by hand. At the +45 band, 100 kg x $3.70 = $370.00, and $370.00 / $4.90 = 75.510 kg, which rounds up to 76.0 kg. At 75.5 kg the +45 charge is $369.95, still cheaper; at 76.0 kg it is $372.40, so the 100 kg charge of $370.00 wins.

The exporter ships three consignments in one week. The warehouse measures in inches, so the volume weight uses 366 cubic inches per kilogram.

• Bulky cartons, volume-rated: six cartons of 24 x 20 x 18 in, 21.5 kg each. Volume is 8,640 in3 x 6 = 51,840 in3, and 51,840 / 366 = 141.639 kg, rounded to 142.0 kg. Gross is 129.0 kg, so chargeable weight is 142.0 kg in the +100 band: 142.0 x $3.70 = $525.40. Rating on gross weight would have shown $477.30.
• Dense crates, break-rated: two crates of machined parts, 78.6 kg gross, rounded to 79.0 kg, with a small volume. At +45 the charge is 79.0 x $4.90 = $387.10. Billed as 100 kg at $3.70 it is $370.00, which is $17.10 or 4.4% lower, so the AWB shows 100.0 kg chargeable.
• Small parcel, minimum-rated: one box at 11.2 kg, rounded to 11.5 kg. At -45 the charge is 11.5 x $6.40 = $73.60, below the $85.00 minimum, so $85.00 is billed.

The same carton set measured in pounds would come to 51,840 / 166 = 312.289 lb, rounded to 313 lb. If the forwarder's card from a US origin is quoted per pound, the bands and break points must be recomputed in pounds; do not convert a per-kilogram break point and assume it lands on the same consignments.

Worked India export: a bulky consignment crosses the 100 kg break

The Chennai consignment from the opening shows how volume weight and a break point combine. Gross weight alone would put it in the +45 band; volume weight pushes it past the point where the +100 break is cheaper.

Four cartons each measure 62.4 x 48.5 x 40.2 cm and weigh 14.8 kg. Gross is 59.2 kg, rounded to 59.5 kg. Rounded dimensions are 62 x 49 x 40 cm, or 121,520 cm3 per carton. The consignment volume is 486,080 cm3, and 486,080 / 6,000 = 81.013 kg, rounded to 81.5 kg. Chargeable weight is therefore 81.5 kg.

The gross-only line explains why shippers are sometimes surprised by air invoices: the scale ticket under-describes what the aircraft carries. The other lines show the two errors a buyer can recover. Per-piece rounding added 0.5 kg, and ignoring the break point added ₹1,060 on top. Across, say, 300 consignments a year that land between 77.5 kg and 99.5 kg, an average miss of ₹900 would cost ₹2,70,000; the figures are illustrative, so rebuild them from your own shipment history.

How the rate line appears on the air waybill and the FWB message

The air waybill's rating block records the result of everything above, so it is the field set to audit against. Gross weight, rate class, commodity item number, chargeable weight, rate and total sit in fixed boxes on the paper form and in the RTD rate description line of the electronic FWB message.

The e-AWB handling guideline published by the Australian e-AWB working group on IATA's site lists the RTD fields: line number, number of pieces, weight code K, gross weight, rate class code (C, M, N or Q), commodity item number, chargeable weight, rate or charge, and total charge. It also states that a C rate class requires the commodity item number. Following that pattern, the Chennai consignment's line would carry 4 pieces, gross 59.5 kg, rate class Q, chargeable weight 100.0 kg, rate 185.00 and total 18,500.00.

Two layers of rating exist on a consolidated shipment. The airline rates the master air waybill on the forwarder's consolidated weight, and IATA's Cargo Accounts Settlement System is the billing and settlement framework many airlines and forwarders use between themselves. The shipper is billed on the house air waybill under its own contract with the forwarder. A break point earned on the master never reaches the shipper unless the house rating applies it too.

Our air waybill extraction pilot describes how to capture these boxes reliably from scanned documents. The audit rule here is narrower: once the rate line is captured, re-rate it from gross weight, dimensions and the contracted card, and compare totals.

Incident trace: a consolidator invoice billed at the wrong break

The Chennai invoice was caught by an automated re-rate, not by a person reading the PDF. The sequence below shows which record exposed each error and how long the correction took.

1. Monday 10:40, dispatch: the shipper's warehouse closes delivery note DN-CHN-26-4471 with 4 cartons, 59.2 kg on the dispatch scale and dimensions keyed from the carton specification in the item master.
2. Monday 17:15, acceptance: the forwarder's acceptance team measures the cartons, keys 20.5 kg of volume weight per carton into the house air waybill HAWB MAA-26-08817, and rates 82.0 kg at the +45 rate of ₹240.
3. Thursday 09:05, invoice receipt: invoice FI-26-11392 arrives through the e-invoice inbox and posts to the freight audit queue as freight line ₹19,680 against HAWB MAA-26-08817.
4. Thursday 09:06, re-rate: the audit job rebuilds volume weight from the delivery note dimensions (81.013 kg, rounded to 81.5 kg), finds the 77.5 kg break point on the contracted card and rates 100.0 kg at ₹185, totalling ₹18,500. Variance ₹1,180 exceeds the ₹200 tolerance, so the line is held.
5. Thursday 15:30, dispute: the analyst sends the re-rate worksheet; the forwarder agrees and issues credit note CN-26-0412 for ₹1,180 the following Monday, and the invoice is approved net.

Without the item-master dimensions, the audit job could only have flagged the per-piece rounding if the forwarder had sent its own measurements. Shippers who never record carton dimensions cannot rerun volume weight, and end up arguing about rates instead of weights.

Air freight invoice audit re-rates each house air waybill line in the freight audit queue from dispatch gross weight, item-master dimensions and the contracted weight-break card, applying TACT Rule 3.9.4 rounding and the higher-break comparison, and holds any line whose variance exceeds a set tolerance such as ₹200 or $5.

Audit checks a rating engine can enforce and where a buyer decides

Most weight-break checks are arithmetic and should run on every invoice line without a person. Judgement is needed where the inputs disagree, such as a forwarder's measurement against the shipper's master data, or where a card's terms are ambiguous.

Commodity item rates need extra care. TACT Rule 3.3, as reproduced in the ASEAN material, gives specific commodity rates precedence over class rates and general cargo rates, but allows a lower general rate to be used except where the commodity rate was set for items covered by a class rate. A rating engine can list eligible items; matching the goods to the item description is a person's call.

Negotiating a weight-break card that fits your shipment profile

The cheapest card is the one priced for the weights you actually ship. Build the shipment profile first, then negotiate the bands that carry most of the spend rather than the headline rate.

A simple profile groups last year's consignments by lane and chargeable-weight band, with count and spend per band. Freight buyers handling heavier lanes should also read our note on freight density calculation, because dense and bulky goods respond differently to a change in divisor or break structure. Ask for the full card, including its validity dates and surcharge basis, before comparing offers.

Run the old and new cards against the same profile before signing. A new card that cuts the +100 rate from ₹185 to ₹180 but lifts the -45 rate from ₹310 to ₹330 adds ₹560 to every 28 kg consignment, which outweighs the saving for a shipper whose orders are mostly small. Our logistics and supply chain hub collects related guides on freight rating and audit.

Weight-break discipline needs three things on file: carton dimensions in the item master, the contracted card with its breaks, and a re-rate step before invoice approval. With those in place, the audit is a calculation rather than a negotiation.

• Record dimensions once: store outer carton dimensions and gross weight per pack configuration, and update them when packaging changes.
• Load the full card: keep every break, the minimum and the validity dates in the rating table, not just the headline rate.
• Re-rate before paying: compare each invoice line with a rebuilt charge and hold variances above a set tolerance.
• Review the profile quarterly: check where consignments cluster against break points and bring the result to the next rate negotiation.

Freight buyers negotiating air freight weight-break cards should test each card in the procurement rate table against a twelve-month consignment profile, confirming the minimum-charge threshold, the 6,000 cm3 per kg divisor and higher-break rating, because a ₹5 cut in the +100 rate cannot offset a ₹20 rise in the -45 rate for 30 kg consignments.

If you want a rating and invoice-audit workflow scoped around your own lanes and forwarders, you can describe it through our request for proposal form. Include a sample of rate cards and a quarter of invoices so the break points can be tested against real consignments.