About

Miscalculating container loads costs real money. An underloaded 40ft container wastes 30m³ of paid volume. Overloading past the rated payload of 26,680 kg triggers port rejections, fines, and structural risk to the chassis. This calculator solves the 3D bin-packing problem for standard ISO 668 intermodal containers. It applies a First Fit Decreasing Height algorithm to determine how many uniform cartons fit inside a given container, respecting dimensional constraints, stacking limits, and maximum gross mass. Volumetric utilization and floor coverage are reported as percentages.

The tool assumes rigid rectangular cargo with uniform dimensions. It does not account for palletization, internal bracing, or irregular load shapes. Weight distribution across the container floor is assumed uniform. For refrigerated (reefer) containers, subtract approximately 10cm from internal length for the cooling unit. Pro tip: always verify the tare weight stamped on the container door - it varies by manufacturer and age.

Formulas

The calculator determines the maximum number of cargo units that fit inside a container using layer-based bin packing. For each candidate orientation of the cargo box, the algorithm computes how many fit per layer and how many layers stack vertically.

N_layer = floor(L_cl) × floor(W_cw)

N_stack = floor(H_ch)

N_total = N_layer × N_stack

Where L_c, W_c, H_c are the internal container dimensions and l, w, h are the cargo box dimensions in the chosen orientation. The algorithm tests all 6 permutations of (l, w, h) unless orientation is locked (e.g., "this side up").

U_vol = N_total × l × w × hL_c × W_c × H_c × 100%

Weight constraint: N_total × m ≤ P_max, where m is the mass per unit and P_max is the container's maximum payload capacity. If exceeded, N_total is reduced to floor(P_max ÷ m).

Reference Data

Container Type	External L × W × H	Internal L × W × H (mm)	Door W × H (mm)	Capacity (m³)	Max Payload (kg)	Tare Weight (kg)	Max Gross (kg)
20ft Standard	6,058 × 2,438 × 2,591	5,898 × 2,352 × 2,393	2,340 × 2,280	33.2	25,000	2,300	30,480
40ft Standard	12,192 × 2,438 × 2,591	12,032 × 2,352 × 2,393	2,340 × 2,280	67.7	26,680	3,800	30,480
40ft High Cube	12,192 × 2,438 × 2,896	12,032 × 2,352 × 2,698	2,340 × 2,585	76.3	26,460	4,020	30,480
45ft High Cube	13,716 × 2,438 × 2,896	13,556 × 2,352 × 2,698	2,340 × 2,585	86.0	27,600	4,800	32,400
20ft Open Top	6,058 × 2,438 × 2,591	5,898 × 2,352 × 2,346	2,340 × 2,233	32.6	21,700	2,360	30,480
40ft Open Top	12,192 × 2,438 × 2,591	12,032 × 2,352 × 2,346	2,340 × 2,233	66.5	26,330	4,150	30,480
20ft Flat Rack	6,058 × 2,438 × 2,591	5,698 × 2,230 × 2,255	-	28.6	27,400	2,870	30,480
40ft Flat Rack	12,192 × 2,438 × 2,591	12,064 × 2,230 × 1,955	-	52.5	39,200	5,280	45,000
20ft Reefer	6,058 × 2,438 × 2,591	5,444 × 2,294 × 2,271	2,286 × 2,195	28.4	21,520	3,080	30,480
40ft Reefer HC	12,192 × 2,438 × 2,896	11,577 × 2,294 × 2,557	2,286 × 2,502	67.5	26,280	4,200	30,480
20ft Tank	6,058 × 2,438 × 2,591	- (cylindrical)	-	24.0	26,010	3,070	30,480
Pallet-Wide 45ft	13,716 × 2,500 × 2,896	13,556 × 2,444 × 2,698	2,426 × 2,585	89.2	27,200	5,200	32,400

Frequently Asked Questions

Each box has 6 possible orientations (3 axes × 2 rotations). The calculator tests all 6 permutations of length, width, and height against the container interior and selects the orientation yielding the highest count. If you enable "This Side Up," only 2 orientations are tested (the height axis is locked), which can reduce capacity by 5-15% depending on box proportions.

Manual calculations often ignore the floor() function. For example, a container 12,032 mm long with 600 mm boxes gives 20.05 - you can only fit 20, not 21. This rounding loss compounds across all three axes and across orientations. The calculator also enforces the weight limit, which may cap the count below the volumetric maximum.

No. This calculator works with loose carton/box loading. If you use pallets (standard EUR pallet is 1,200 × 800 mm, US pallet is 1,219 × 1,016 mm), enter the full pallet footprint including overhang as your cargo dimensions and the stacked pallet height as the cargo height.

Floor utilization measures what percentage of the container's floor area (L × W) is covered by cargo footprints. Volumetric utilization measures total cargo volume divided by total container volume. A tall, narrow load may have 90% floor use but only 50% volume use if it doesn't stack to the ceiling.

Internal dimensions follow ISO 668 and ISO 1496-1 standards for general-purpose containers manufactured after 2000. Actual internal dimensions vary by ±10 mm due to corrugation depth and manufacturer tolerances. For critical loads, measure the specific container assigned to your shipment.

No. The maximum payload is a structural and regulatory limit. Exceeding it risks chassis failure, port rejection, and violates SOLAS (Safety of Life at Sea) VGM requirements. Since July 2016, shippers must declare Verified Gross Mass before loading. The calculator caps the count at the weight limit and flags the constraint.