A How the count is worked out
For one orientation the answer is three whole-number divisions multiplied together. Use the container's inside dimensions and the carton's outer dimensions in the same unit:
cartons = ⌊inside length ÷ carton length⌋ × ⌊inside width ÷ carton width⌋ × ⌊inside height ÷ carton height⌋
⌊ ⌋ = round down: half a carton does not fit
A carton can face six ways (three if two sides are equal), so the calculator tries each and keeps the best. Most online "how many boxes fit" tools stop there. That one-orientation stack leaves a strip at the side wall, a gap under the roof and a gap at the door, each narrower than the carton as placed but often wide enough for a carton turned another way. The calculator fills those spaces too: it places the best block, then treats each leftover space as a smaller box and packs it again, in any orientation, until nothing more fits. Every count is a real arrangement listed under Stacking plan, so a loader can follow it.
With This side up ticked, cartons keep their height vertical and only turn on the floor (length and width swapped). Pallets, mixed carton sizes, crush strength and weight distribution are not modelled.
B Worked example: 50 × 40 × 30 cm in a 20' GP
20' GP inside: 589.8 × 235.2 × 239.3 cm (SeaCube specification, see containers used). One carton: 0.06 m³, 12 kg.
- One orientation, upright (40 cm along the box, 50 cm across, 30 cm high): ⌊589.8 ÷ 40⌋ × ⌊235.2 ÷ 50⌋ × ⌊239.3 ÷ 30⌋ = 14 × 4 × 7 = 392 cartons. This is the figure most calculators give. It leaves a 35.2 cm strip along one wall and fills 71% of the box.
- Turned cartons: lay the main block as 19 × 4 × 5 = 380 cartons (30 along, 50 across, 40 high), then fill the 35.2 cm side strip with 14 × 1 × 4 = 56 cartons on their sides and the 39.3 cm gap under the roof with one more layer of 14 × 4 = 56 laid flat: 492 cartons, 89% of the inside volume.
- Volume only at 85%: 33.2 m³ × 0.85 ÷ 0.06 = 470 cartons.
- Weight: 28,340 kg payload ÷ 12 kg = 2,361 cartons, so space is the limit, not weight.
- 1,000 cartons: three 20' GPs either way (1,000 ÷ 492 = 2.03), or a single 40' HQ, which takes up to 1,150.
If the cartons must stay upright, the side strip is too narrow for a 40 or 50 cm footprint and the answer stays at 392. That difference, about one carton in five, is why the orientation rule printed on the carton matters as much as its size.
C Common carton sizes
Counts from this calculator for the default containers, with cartons touching (no clearance). Each cell is upright / any orientation; the volume figure at 85% is in brackets.
| Carton (cm) | m³ each | 20' GP | 40' GP | 40' HQ |
|---|
| 60 × 40 × 40 | 0.096 | 255 / 261 (293) | 550 / 560 (599) | 660 / 660 (676) |
| 60 × 40 × 30 | 0.072 | 357 / 393 (391) | 770 / 830 (799) | 880 / 920 (901) |
| 60.96 × 40.64 × 30.48 (24 × 16 × 12 in) | 0.0755 | 357 / 393 (373) | 742 / 808 (762) | 848 / 902 (859) |
| 50 × 40 × 30 | 0.060 | 392 / 492 (470) | 840 / 1,040 (959) | 960 / 1,150 (1,081) |
| 45 × 35 × 25 | 0.0394 | 720 / 782 (716) | 1,530 / 1,610 (1,461) | 1,700 / 1,854 (1,648) |
| 40 × 30 × 30 | 0.036 | 763 / 774 (783) | 1,610 / 1,630 (1,598) | 1,840 / 1,840 (1,802) |
| 40 × 30 × 20 | 0.024 | 1,199 / 1,269 (1,175) | 2,530 / 2,630 (2,398) | 2,990 / 2,990 (2,704) |
Where the upright figure is higher than a plain grid (for example 357 against 315 for 60 × 40 × 30 cm in a 20' GP), part of the floor is laid with the carton turned 90°. Where the volume figure is higher than the stack, the carton shape wastes space in that box; where it is lower, the stack is tight and the 85% rule is cautious.
D Why a real load fits fewer
- Clearance. Loaders need a few centimetres under the roof to slide the top layer in, and the doors must close. Corrugated walls are narrower at the ribs than the published inside width.
- Carton bulge and tolerance. Measure the packed carton, not the drawing. If 50 × 40 × 30 cm cartons bulge to 52 × 42 × 32 cm, the upright stack in the 20' GP is still 392, but the turned-carton count falls from 492 to 392: the gaps that held the extra cartons are gone.
- Stacking strength. Heavy or soft cartons cannot go seven high. Check the box maker's stacking load and the "max stack" mark.
- Weight and balance. Dense goods hit the payload or the road limit first, and the weight must be spread along the floor.
- Pallets. Palletised cartons lose the pallet height and the gaps around each pallet; see pallets per container.
So the stack count is a ceiling. For a purchase-order quantity, ask the forwarder or loading warehouse for a load plan with your measured cartons.
E Containers used
The default 20' GP, 40' GP and 40' HQ are the same boxes as the CBM worksheet: SeaCube Containers' 20' dry, 40' standard dry and 40' high cube dry specifications (read 21 October 2026).
| Type | Inside L × W × H | Door W × H | Max payload |
|---|
| 20' GP | 5,898 × 2,352 × 2,393 mm | 2,340 × 2,280 mm | 28,340 kg |
| 40' GP | 12,032 × 2,352 × 2,393 mm | 2,340 × 2,280 mm | 28,860 kg |
| 40' HQ | 12,032 × 2,352 × 2,698 mm | 2,340 × 2,585 mm | 28,750 kg |
Field 8 adds a 45' HC, reefer or open top using the reference values on the container dimensions data sheet (ONE and CMA CGM figures). Inside sizes differ by a few centimetres between owners, makers and ages of box, and a few centimetres can change a count by a whole row, so check the box you are booking when it is tight.
F Questions
How many cartons fit in a 20ft container?
It depends entirely on the carton size. In the 20' GP used here (5,898 × 2,352 × 2,393 mm inside), 50 × 40 × 30 cm cartons stack 392 in one orientation and up to 492 when turned cartons fill the gaps; 60 × 40 × 40 cm cartons give 225 to 261; 40 × 30 × 20 cm cartons give 1,078 to 1,269. Enter your own carton size for the figure that applies.
How many cartons fit in a 40ft or 40ft high cube container?
With the same 50 × 40 × 30 cm carton: 840 in one orientation and up to 1,040 in a 40' GP, and 1,050 to 1,150 in a 40' HQ. The high cube's extra 305 mm of height often adds a whole layer.
Why is the mixed-orientation count higher than the one-orientation count?
Stacking every carton the same way leaves strips along the walls, the roof and the door that are narrower than the carton. Turning cartons so a shorter side faces the strip often fits another row or layer. The calculator tries every orientation for the main block and for each leftover space.
What if my cartons must stay upright?
Tick This side up. Cartons then keep their height vertical and are only turned on the floor, which is what fragile goods, liquids and many printed cartons require. The count is usually lower.
Why can the count be higher than the volume at 85% figure?
The stacking count is a geometric maximum with cartons touching each other and the walls. A real hand load needs a little clearance and cartons bulge, so plan on somewhat fewer, and ask your forwarder for a load plan before you fix the quantity on a purchase order.
Does the calculator check the weight limit?
Yes, if you enter the gross weight per carton. The count is capped at the container's maximum payload divided by that weight, and the card says when weight, not space, is the limit. Road weight limits are often lower than the container rating.
Can I mix carton sizes?
This page counts one carton size. For a packing list with several sizes, use the CBM worksheet on the home page: it totals the volume and weight of every line and compares them with each container.