The number of cartons that fit in a container is found with per-axis grid math: divide the container's inner length, width and height by the carton dimensions, round each down, and multiply the results. A 60 × 40 × 40 cm carton fits 225 times in a 20ft, 500 times in a 40ft and 600 times in a 40HC. That count must then be checked against weight (payload) and carton stacking strength.
Why dividing volumes misleads
The quick method many people use is container volume divided by carton volume. For a 0.096 m³ carton in a 20ft container (33.2 m³) that gives about 345 cartons. You will never load that many, because cartons cannot be cut to fill the 498 mm gap at the end, 352 mm at the side and 393 mm under the roof. Volume division is an upper bound, not a load plan. For total shipment volume, see how to calculate CBM.
Per-axis grid math
Take the inner dimensions from the catalogue (typical values; check the CSC plate of the actual unit):
- 20GP: 5,898 × 2,352 × 2,393 mm
- 40GP: 12,032 × 2,352 × 2,393 mm
- 40HC: 12,032 × 2,352 × 2,698 mm
For a 600 × 400 × 400 mm carton in a 20GP, with the 600 mm side along the container's length:
- Length: 5,898 ÷ 600 = 9.83 → 9
- Width: 2,352 ÷ 400 = 5.88 → 5
- Height: 2,393 ÷ 400 = 5.98 → 5
- Total: 9 × 5 × 5 = 225 cartons
Orientation changes the answer
A carton has six orientations: any of its three sides can be the height, and each can be rotated 90° on the floor. For the same carton, turning the 600 mm side across the width gives 14 × 3 × 5 = 210 cartons, fifteen fewer. For a 500 × 400 × 300 mm carton in a 40HC, the 400 × 300 × 500 orientation (400 along the length, 300 across, 500 upright) gives 30 × 7 × 5 = 1,050 cartons, whereas the "as listed" 500 × 400 × 300 orientation gives only 24 × 5 × 8 = 960.
Single-orientation grid results
| Carton (mm) | 20GP | 40GP | 40HC |
|---|---|---|---|
| 600 × 400 × 400 (0.096 m³) | 225 (9×5×5) · 65% | 500 (20×5×5) · 71% | 600 (20×5×6) · 75% |
| 500 × 400 × 300 (0.06 m³) | 392 (14×4×7) · 71% | 840 (24×5×7) · 74% | 1,050 (30×7×5) · 83% |
| 450 × 350 × 300 (0.04725 m³) | 570 · 81% | 1,200 · 84% | 1,400 · 87% |
The percentage is carton volume divided by inner container volume. Note the 600 × 400 × 400 carton in a 20GP, which fills only 65%: its size simply does not suit 20ft inner dimensions. For a fuller comparison of container types, see 20ft vs 40ft vs 40HC.
Beware of grids that fit too tightly
The 500 cartons in a 40GP come from 20 cartons × 600 mm = 12,000 mm, just 32 mm short of the 12,032 mm inner length. If mass-produced cartons bulge by only 2 mm to 602 mm, twenty of them need 12,040 mm and no longer fit. The row drops to 19 and the total to 19 × 5 × 5 = 475 cartons, 25 fewer. Re-measure cartons from the actual production run and allow a tolerance before you promise a quantity to a buyer.
Worked example: adding a mixed block
Stay with the 600 × 400 × 400 carton in a 20GP. After a main block of 9 cartons covering 5,400 mm, 498 mm remain at the door end. That is enough for one row of cartons turned so that their 400 mm side runs along the container:
- Remaining length: 498 ÷ 400 → 1 row
- Width: 2,352 ÷ 400 → 5 columns (400 mm side across)
- Height: 2,393 ÷ 600 → 3 tiers (600 mm side upright)
- Extra: 1 × 5 × 3 = 15 cartons
The total becomes 240 cartons (23.04 m³, about 69% of inner volume), provided the cartons may stand on their 600 mm side and can still take three tiers in that position. Combinations like this get complicated quickly once you have several blocks, side gaps and "do not invert" rules. That is where the Cartons per Container Calculator and the planner save time.
Check weight against payload
A count that fits by space may not be allowed by weight. Multiply cartons by gross weight per carton:
- 600 × 400 × 400 cartons at 25 kg × 600 cartons in a 40HC = 15,000 kg, comfortably below the typical 26,540 kg payload.
- 500 × 400 × 300 cartons of liquid at 30 kg × 1,050 cartons in a 40HC = 31,500 kg, which exceeds the 26,540 kg payload. Weight allows only 884 cartons (26,520 kg).
In the second case a 20ft container, or two containers, may make more sense. Remember road limits too: in Indonesia, the permitted truck weight and road class often bind before container payload does. See the glossary entry for payload and the VGM SOLAS guide. Any calculation is a simulation; the verified gross mass (VGM) must still come from official weighing.
Stacking strength and weight distribution
In a six-tier stack of 25 kg cartons, the bottom carton carries 5 × 25 = 125 kg, plus the shocks of the sea voyage and road legs. Ask your box supplier for compression data (such as BCT), apply an agreed safety factor for humidity and journey length, and limit the number of tiers where needed. Heavy cartons go at the bottom, and the cargo's centre of gravity should stay close to the middle of the container; see centre of gravity and weight distribution. Fill remaining voids with dunnage or airbags so cartons cannot shift.
Mixed-SKU loads
When one container carries several SKUs, there is no single formula. A practical approach:
- Group cartons with equal heights, or heights that are multiples, so each layer stays level.
- Load the heaviest, strongest SKUs on the floor first and light SKUs on top.
- Build in walls from the front end to the doors so the unloading sequence works.
- For palletised goods, calculate cartons per pallet first, then pallets per container. Use the Cartons per Pallet Calculator and how many pallets fit in a container.
Common mistakes
- Dividing volumes instead of running a grid. The result is always too optimistic.
- Trying only one orientation. The difference between orientations can be tens or hundreds of cartons.
- Using outer container dimensions (6,058 mm for a 20ft) instead of inner ones.
- Forgetting the door opening. Tall cartons or pallets must clear a 2,280 mm door (20GP/40GP) or 2,585 mm (40HC).
- Leaving no tolerance. A zero-clearance grid on paper is hard to load in practice; leave a few centimetres for hands, forklifts and bulging cartons.
- Ignoring weight and stacking strength because the carton count "fits".
Why use the calculator and planner
Hand-worked grid math is fine for one SKU in one orientation. Once leftover space, mixed orientations, tier limits, several SKUs and weight checks come in, manual counts drift. Use the Cartons per Container Calculator for a quick count, then open the 3D load planner to see the stacking pattern, loading sequence, centre of gravity and total weight. A plan remains a simulation; it does not replace VGM, official weighing or operator approval.