How much bulk cargo fits in a 20ft container?

Almost always the payload decides, not the volume. A 20GP carries about 28 tonnes, so the volume of bulk cargo that fits is 28,000 divided by the bulk density: about 35 m³ of wheat (800 kg/m³), 47 m³ of plastic pellets (600 kg/m³ — actually volume-limited to about 30 m³), or only about 18 m³ of sand (1,550 kg/m³).

Why is a 20ft better than a 40ft for dense cargo?

Both containers share almost the same payload ceiling (about 28 tonnes), so a 40ft adds volume you cannot use while costing more freight. The break-even density tells the story: a 20GP balances weight and volume at about 849 kg/m³, a 40HQ at about 375 kg/m³. Anything denser than roughly 850 kg/m³ belongs in a 20ft.

What is a container liner?

A container liner is a large PE or woven PP bag fitted inside a standard dry container, turning it into a clean bulk vessel for grain, sugar, plastic pellets or powders. It protects cargo from moisture and contamination, speeds up loading (pneumatic or conveyor) and discharge (tilt the container and gravity-feed), and removes the need for individual bags.

How do you secure bulk cargo at the door end?

With a bulkhead: a steel or timber barrier (often called a grain door) fixed across the container a short distance from the doors, rated to hold the full thrust of the cargo shifting forward under braking. The liner is attached to the bulkhead, and the doors stay closed behind it as a second barrier. Never rely on the container doors alone to hold back bulk cargo.

Bulk Cargo Container Loading — Payload, Liners and Methods

Bulk cargo — grain, sugar, plastic pellets, fertiliser, minerals, scrap — plays by different rules than boxed cargo. Space is almost never the problem: weight is. This page covers the payload math, why dense cargo belongs in a 20ft, how container liners turn a standard box into a bulk vessel, and the loading and securing methods that keep both the cargo and the container intact.

1. The golden rule: dense cargo is weight-limited

Every container type has a density break-even — the cargo density at which the weight limit and the space limit arrive at exactly the same time:

Type	Nominal capacity	Payload ceiling (reference)	Density break-even	Meaning
20GP	33.2 m³	≈ 28,000 kg	849 kg/m³	Denser than this → weight decides
40GP	67.7 m³	≈ 28,000 kg	425 kg/m³	Most bulk commodities are far denser than these numbers
40HQ	76.3 m³	≈ 28,000 kg	375 kg/m³
45HQ	86.1 m³	≈ 27,700 kg	320 kg/m³

Why the 20ft usually wins for bulk: a 40ft costs noticeably more freight than a 20ft but carries the same 28 tonnes. Anything denser than ~850 kg/m³ fills a 20GP by weight before it's full by volume — the extra 34 m³ of a 40ft is air you're paying to ship. Bulk exporters run 20ft boxes almost exclusively for exactly this reason.

2. Quick capacity figures for common bulk commodities

Commodity	Bulk density	In a 20GP (28 t payload)	Limited by
Wheat / grain	≈ 770 – 830 kg/m³	≈ 34 – 36 m³ — nearly full	Weight and volume arrive together
Sugar	≈ 800 kg/m³	≈ 35 m³ — nearly full	Weight and volume arrive together
Plastic pellets (PP/PE)	≈ 550 – 650 kg/m³	28 t ÷ 600 ≈ 47 m³ needed → fills the full ≈ 33 m³ at ≈ 20 t	Volume (lightest common bulk)
Fertiliser (urea)	≈ 720 – 800 kg/m³	≈ 35 – 39 m³ — nearly full	Weight, roughly at full volume
Sand / aggregates	≈ 1,400 – 1,600 kg/m³	≈ 18 – 20 m³ — box only ~55% full	Weight, hard
Cement	≈ 1,200 – 1,500 kg/m³	≈ 19 – 23 m³	Weight, hard
Steel scrap / briquettes	≈ 2,000+ kg/m³	≈ 14 m³ or less	Weight, and floor load limits

Use your own measured bulk density — moisture swings grain density by ±10%, and compaction during loading can add 5–8% more. The formula never changes: loadable volume = payload ÷ bulk density, capped by container volume.

3. Container liners: a dry box becomes a bulk vessel

What a liner does

A container liner is a giant PE film or woven PP bag fitted inside a standard 20ft or 40ft box, sealed to a steel or timber bulkhead at the door end. It keeps food-grade cargo clean, blocks moisture and container sweat, lets you load by conveyor or pneumatic pipe, and discharge by tilting the box and letting gravity do the work — no bagging, no pallets, no hand unloading.

Common liner types

Type	Best for
PE film liner	Grain, sugar, plastic pellets — cheap, food-grade, single use
Woven PP liner	Fertiliser, minerals, abrasive products — tear-resistant
Barless / bar-in liner	With or without steel retaining bars at the bulkhead, by cargo thrust
Thermal liner	Temperature-sensitive cargo (not truly bulk, but same fit-out)

Loading and discharge methods

Method	How it works
Conveyor / belt thrower	A high-speed belt throws grain or pellets to the far end; standard for grain, fills the box evenly in under an hour
Pneumatic	Powders and pellets blown in through a pipe — clean and fast, needs a compressor rig
Gravity + tilt	Silo overhead, container tilted slightly; also the standard discharge method at destination with a tilt chassis
Grab / bobcat	Scrap and minerals — watch the floor load and wall damage, use protective boards

4. Weight distribution: the rules that protect the box

Spread the load, respect the floor rating

Container floors are rated for an evenly spread payload, not point loads. Bulk cargo self-levels, which helps, but dumped-in minerals and scrap can concentrate tonnes on a few square centimetres and punch through the plywood. Load heavy cargo gently, in layers, and never drop it from height into one spot.

The bulkhead is not optional

Under emergency braking, 28 tonnes of grain pushes forward with enormous force. Container doors alone are not designed to hold that. A rated bulkhead (grain door) across the door end carries the thrust, the liner seals to it, and the closed doors behind it are only the second line of defence. Open a loaded bulk container standing to the side, never in front of the doors.

Moisture is the silent killer

Grain above ~14% moisture heats and moulds in transit; container sweat drips from the roof on any lane with big day-night temperature swings. Use dry cargo, liners, desiccant poles, and avoid loading in the rain — a rejected bulk shipment has no cheap way home.

⚠️ Confirm the payload with the carrier, every time. The ≈ 28 t figure is the structural ceiling of a standard box; shipping lines apply lower limits by trade lane, season and inland-leg regulations (road weight limits at destination often bite harder than the ship's). Planning against the theoretical number is how containers get refused at the gate.

5. Frequently asked questions

How many tonnes of grain fit in a 20ft container?: About 26–28 tonnes, and conveniently that's also very close to a full box by volume — grain at ~800 kg/m³ sits right at the 20GP break-even of 849 kg/m³. It's one of the few commodities where a 20ft is both full and at weight.
Can I use a 40ft for bulk if freight rates are similar?: For genuinely light bulk it can pay: plastic pellets at ≈ 600 kg/m³ fill a 20GP at only ≈ 20 t (volume-limited), while a 40HQ takes ≈ 46 m³ before hitting the same 28 t — about 40% more cargo per box. But anything denser than the box's break-even (425–375 kg/m³ for 40ft types) gains nothing. Check the break-even density against your commodity before booking anything bigger than a 20ft.
Do I need food-grade containers for grain?: Yes — lines designate clean, dry, odour-free "food grade" boxes for edible cargo. Inspect before loading: no residues, no rust flakes, no smells, door seals intact. A liner adds a second barrier and is standard practice for grain and sugar.
What about moisture-sensitive powders?: Combine a PE liner with desiccant poles sized to the lane (rule of thumb: 8–12 poles per 20ft through the tropics), and keep dwell time at humid ports short. Powders that cake with moisture (cement, some fertilisers) also need the box loaded and sealed the same day the liner goes in.
How do I check the weight plan for bagged or palletized portions of the cargo?: Bagged bulk (25/50 kg bags, big bags) behaves like ordinary cargo — enter the bag or big-bag dimensions, weight and quantity in the Container Loading Calculator and it returns the count, layout, loading rate and total weight per container. No installation required.

Shipping bagged or palletized bulk? Enter the dimensions and get the exact count and layout

Open the Container Loading Calculator →