IMDG 4.2.1.9 Fill Rules

ISO Tank Loading Calculator

Know your true loadable mass before the surveyor walks the gantry.

A misread on any one of the four binding limits in IMDG Code Chapter 4.2 ends the same way. The container sits, the demurrage clock runs, and the booking unwinds at your cost. This calculator works the four limits in order so you see which one governs your specific cargo and tank, and what to do when it bites.

  • Thermal-expansion fill cap (4.2.1.9.2)
  • Hard ceiling at 95% or 97%, set by hazard class (4.2.1.9.4)
  • Weight cap, calculated as MGW minus tare
  • The 20% to 80% surge floor for tanks above 7,500 L (4.2.1.9.1.1)

Density, expansion coefficient, and vapour pressure come straight off SDS Section 9. UN class and packing group come off Section 14. Type the numbers in once. The result names the governing constraint, calls out any surge violation, and recommends a tank or fill that clears it.

The catalogue covers 35 tank build configurations, from T11 stainless through to T75 cryogenic, including PE, PTFE, rubber, and lead-lined variants for the harder cargoes.

For any specific UN entry, the IMDG Dangerous Goods List Columns 13 and 14 is the binding authority. Treat this tool as a fast pre-check, not a substitute for the official text.

Loading drums, IBCs, big bags, or pallets into 20'GP, 40'GP, 40'HC, or reefer containers is a different problem with different math. Use the Container Loading Calculator for that one.

Tank build

Pick a catalogue row and the form prefills capacity, MGW, tare, and MAWP from the typical build for that T-code.

Got a real tank in front of you, with a BV cert on the desk? Choose Custom tank and type those numbers in. Anything you enter in the override fields below takes precedence over the catalogue at compute time, so the calculator runs against your tank, not a typical one.

Read the value off the data plate or BV cert. Type over the prefill any time your tank doesn't match the catalogue typical.

Real tanks come in at 30,480 to 38,000 kg depending on build year and country of operation. Override the default if your data plate reads differently.

Lined and heated builds carry several hundred kilos more than the catalogue typical. Trust the data plate, not the assumption.

The calculator uses this to check that your cargo's 50 deg C vapour pressure stays within the tank's pressure envelope.

Take the value from SDS Section 9. The default of 0.79 is methanol at 20 deg C.

Take the value from SDS Section 9. If it isn't listed, 0.001 per deg C is a safe conservative default for most organics.

Take the value from SDS Section 9. The calculator checks it against your tank's MAWP and warns you well before the rating runs out.

IMDG 4.2.1.9.5 sets the default at 50 deg C. Lift it to 65 deg C for tropical lanes or heated cargoes that travel hot.

Verify by hand

For any cargo or tank you don't already know in your sleep, work the six steps below on paper. The calculator and your handwritten answer should agree within rounding. If they don't, one of your inputs is wrong.

  1. Thermal cap per IMDG 4.2.1.9.2.1: TP = 97 / (1 + alpha × (transitT − fillT))
  2. Hard ceiling per IMDG 4.2.1.9.4: 95% for Class 6.1 PG I/II and Class 5.1 PG I/II. Every other cargo is 97%.
  3. Volumetric cap = MIN(thermal, ceiling) × tank capacity / 100
  4. Weight cap = (MGW − tare) / density
  5. Loadable = MIN(volumetric, weight). The lower of the two is your governing constraint, and the one to argue from when a buyer asks why their order is short.
  6. Surge floor per IMDG 4.2.1.9.1.1: tanks above 7,500 L cannot transit between 20% and 80% fill unless they are baffled or compartmented.

Worked example

You have a parcel of 98% sulphuric acid (UN 1830, SG 1.84) booked into a 24,000 L T11. The weight cap works out to (36,000 − 4,000) / 1.84 = 17,391 L, or 72.5% of tank capacity, which looks fine on paper.

It isn't. That fill sits dead inside the 20% to 80% surge band, and the IMDG rule rejects it on the spot. The choice in front of you is the same it always is: change the cargo, or change the tank.

Move the same parcel into a 21,000 L T14 and the math turns over. Weight cap becomes (36,000 − 4,200) / 1.84 = 17,283 L, or 82.3% fill, which is clear of the 80% surge floor with margin to spare. The load ships.

Second worked example: TiCl4 in a custom tank (BV cert GESU800963-1)

Plug the inputs below into the form above. Your output and the expected output should match line for line.

If they don't, something in the input pipeline has drifted, and the load is worth a second look before the vessel sails.

Inputs

  • Tank build: Custom tank (manual entry)
  • Capacity: 15,864 L
  • MGW: 34,000 kg
  • Tare: 4,660 kg
  • Density: 1.73 kg/L (titanium tetrachloride UN 1838)
  • IMDG class: 6.1, packing group I
  • Cubic expansion coeff (alpha): 0.001 per deg C
  • Fill temperature: 15 deg C; transit temperature: 50 deg C
  • Baffled: no

Expected outputs

  • Thermal cap: 93.7% = 97 / (1 + 0.001 × 35)
  • Hard ceiling: 95% (Class 6.1 PG I per IMDG 4.2.1.9.4)
  • Volumetric cap: 14,868 L = MIN(93.7%, 95%) × 15,864
  • Weight cap: 16,960 L = (34,000 − 4,660) / 1.73
  • Loadable: 14,868 L = 25,720 kg = 25.72 MT
  • Governing constraint: Thermal expansion (volumetric cap below weight cap)

Need the full reference catalogue of every ISO tank type, with T-codes, design variants, and frame sizes? It lives at /iso-tanks.

For the design history, the lining trade-offs, and the deep-sea versus intra-EU split that catches first-time buyers out, the ISO tank container glossary entry walks through it.