Container loading math: how much PSF actually fits a 40HC.

"How much fiber fits in a 40HC?" is a question we get every week, and the answer most buyers find online (general "25-26 tons") is mostly right but misses the 3 things that actually move the number. Here's the real math.

The headline answer

For standard bale-packed PSF (polyethylene-wrapped bales, ~250kg each), a 40HC (40-foot high-cube container) loads:

• Raw white PSF: 25.5-26.5 MT (metric tons) typical, up to 27 MT if compression is tight and bales are flat.
• Dope-dyed or specialty PSF: 24-26 MT. Specialty mills often use larger bales (300-400kg) for cleaner handling, which can reduce total weight per container.
• Bright white optical brightener PSF: 26-27 MT. Tight compression, good packing.

The math (actually do the calculation)

A 40HC internal volume is roughly 67.7 m³ (12.03m × 2.35m × 2.39m). The weight limit is 26.5-27.5 MT depending on the line and the trade lane (some lines cap at 25 MT, some at 27 MT — always check with your forwarder).

The binding constraint is usually weight, not volume. PSF at ~250kg/m³ bale density has a bale volume of about 1 m³ per 250kg, so 26 MT of fiber takes ~104 m³ of bale volume — which is more than a 40HC holds. The bales have to be compressed harder.

A properly compressed PSF bale runs ~400-500kg/m³. At 450kg/m³ average bale density:

• 26 MT of fiber = 57.8 m³ of bale volume
• Available 40HC volume = 67.7 m³
• Stowage efficiency = 85% (typical for fiber bales — some dead air gaps)
• Effective loadable volume = 67.7 × 0.85 = 57.5 m³
• So 26 MT fills the volume almost exactly. The volume ceiling and the weight ceiling meet at about 26 MT.

The 3 things that move the actual number

1. Bale compression

Bale press settings at the mill are the single biggest variable. A 350kg/m³ bale vs a 500kg/m³ bale is a 30% volume difference — and means you might only get 20 MT in the container with the looser press, vs 27 MT with the tighter one. Mills that export regularly know how to set this; mills new to export often over-pack and don't compress enough. Ask your supplier for a "container loading plan" with the bales sized to fit, and request a sample bale to measure.

2. Packaging (PE wrap vs woven + PE)

Most PSF bales are wrapped in polyethylene (PE) film and tied with PP straps. Some specialty packaging adds an outer woven polypropylene (PP) bag for additional protection, which adds ~0.5-1kg per bale in packaging weight and slightly larger bale volume. For sea freight this doesn't change the math much, but for humidity-sensitive shipments (some dope-dyed or low-melt specs), the extra packaging is worth the minor volume penalty.

3. Container weight limit per shipping line

The 40HC's structural limit is ~30.5 MT, but most shipping lines impose a lower "payload" limit, usually 26-27.5 MT for general cargo. Some lines (especially intra-Asia) cap at 25 MT. Always confirm with your forwarder before booking. If the line caps at 25 MT, you can't load 26 MT regardless of container space.

The 3 common mistakes

• Planning for 28 MT and being told 26 MT at the port. Reserve the forwarder-confirmed payload, not the theoretical max.
• Forgetting that 40' standard (non-HC) is 5% less volume. A 40' standard is ~58 m³ vs 40HC's 67.7 m³. That can mean 22-23 MT loaded instead of 26.
• Mixing specs in one container. Some buyers put 2-3 different specs (1.4D + 6D + dope-dyed black) in one 40HC to save freight. The packaging differs, the bales might differ, the stowage gets harder. Usually 1-2 MT less loaded weight, plus segregation/labeling hassle at destination. Fine for LCL consolidation, but expensive for FCL savings.

Quick reference table

The short version

Plan for 25-26 MT per 40HC for PSF. The actual number moves with bale compression, packaging, and your shipping line's payload cap. Ask for a container loading plan from your supplier, and confirm the line's weight limit with your forwarder before you book.