How Much Desiccant Is Required for a 20ft and 40ft Shipping Container? A Complete Container Desiccant Calculation Guide

Few things frustrate an exporter more than opening a container to find rusted parts, mouldy cartons or swollen packaging, with no sign of a leak. The culprit is usually moisture that was already inside the box or formed during the voyage. This guide explains how much container desiccant a 20ft and a 40ft container need, and how to work out the right quantity for your cargo, route and season. 

Why Shipping Containers Need Moisture Control

A sealed steel container is not a dry environment. Cargo, pallets, cartons and even the plywood floor hold water that is released as air temperature changes. Over a sea voyage lasting weeks, a container can pass through tropical heat, cool oceans and monsoon humidity.

Without proper container moisture control that trapped water ends up on your goods. Corrosion, mildew, fungus, label damage and caking are the most common results. Effective cargo moisture protection is far cheaper than a rejected consignment or an insurance dispute, which is why export cargo moisture control has become standard practice for careful shippers.

What Causes Container Rain?

Container rain is the condensation that drips from the roof and walls onto cargo. It happens when warm, humid air inside the container meets a steel surface that has cooled. The air can no longer hold its moisture, so droplets form and fall.

Cargo packed in a hot, humid port and shipped towards cooler waters is especially vulnerable. The temperature swing between day and night adds to the problem. To prevent condensation in shipping containers, you need to lower the amount of water vapour in the air itself. Ventilation alone rarely achieves this, which is why container rain prevention relies on desiccants.

How Container Desiccant Works

A shipping container desiccant is a moisture-absorbing material sealed in a breathable pouch or strip. It draws water vapour from the air and holds it, lowering the dew point inside the container so condensation cannot form.

The main formats built for this job include:

• Cargo Dry Pak: bags combining bentonite clay, calcium chloride and starch in Tyvek, designed to manage moisture and reduce the dew point.
• Sorbipak Strips: hanging strips in 125 gm and 500 gm packs with a hook, offering absorption for up to 60 days, with a 200% absorption capacity.
• Sorbipak Cargo Desiccant: packs in 125 gm and 500 gm, blending silica gel, molecular sieves and calcium chloride.
• Cargo Dry Plus: hanging strips with an absorption capacity of up to 300% of their size.

Used correctly, these cargo desiccant bags and strips act as a dependable moisture absorber for shipping container use, keeping container humidity control consistent from loading to unloading.

Factors That Decide How Much Desiccant You Need

There is no single figure that suits every shipment. The right dose of desiccant for shipping containers depends on several variables:

• Container size: a 40ft container holds roughly twice the air volume of a 20ft.
• Cargo type: hygroscopic goods such as paper, textiles, grains, leather and timber release or absorb far more moisture than metal parts.
• Packaging: cartons, wooden crates and pallets all carry water. Plastic-wrapped goods carry less.
• Voyage duration: a longer transit means more temperature cycles and more moisture exposure.
• Route and season: monsoon crossings and tropical ports demand higher quantities.
• Moisture at loading: damp cargo or a wet floor means extra load for the desiccant.

Container Desiccant Calculation: Step by Step

A practical container desiccant calculation follows a simple sequence.

1. Note the internal volume. A standard 20ft container offers roughly 33 cubic metres, and a 40ft container about 67 cubic metres.
2. Classify the cargo. Decide whether it is moisture-sensitive, moisture-releasing or largely inert.
3. Assess the journey. Consider the route, climate zones crossed and transit time.
4. Choose a baseline quantity. Start with the standard dose for your container size, then adjust upwards for risk.
5. Check the absorption capacity. Confirm how much water each bag or strip can hold, then make sure total capacity comfortably exceeds the expected moisture load.

As a simple example, a 500 gm strip with a 200% absorption capacity can hold up to around 1 kg of moisture. Multiply that by the number of strips used, and you get the total absorption available for the voyage.

How Much Desiccant for 20ft Container

For a standard 20ft container carrying dry, non-sensitive cargo on a short, mild route, a modest quantity of strips or bags is generally enough. As a working guide, this often means a few 500 gm units hung along the walls.

For hygroscopic cargo, long voyages or monsoon-season shipping, the quantity should be increased, often doubled. The question of how much desiccant for 20ft container loads is always answered by cargo and route first, then by size.

How Much Desiccant for 40ft Container

A 40ft container has about twice the air volume and a longer wall and roof surface, so condensation risk is spread over a greater area. Quantities therefore need to be roughly double those of a 20ft box for comparable cargo and conditions.

Many exporters ask how much desiccant for 40ft container shipments with mixed or high-value goods. In these cases, use more units, distribute them evenly and consider combining hanging strips with floor-level bags for full coverage.

These figures are general guidance only. For precise advice on your cargo, send our team your container size, cargo details and route.

Placement Tips That Improve Performance

Even the correct quantity can underperform if placed badly.

• Hang strips from the container’s corrugated side walls, using the hooks supplied, so they sit above the cargo.
• Place bags on top of cartons or in void spaces rather than on the floor.
• Spread units evenly along the length of the container rather than clustering them at the doors.
• Install desiccants just before closing the doors, keeping the packs sealed until use.
• Make sure the container floor and cargo are as dry as possible at loading.

Choosing Between Bags, Strips and Bulk Packs

Hanging strips suit general cargo and cover wall areas efficiently. Desiccant bags for export containers are ideal for placing among cartons or in gaps. For forwarders, manufacturers and exporters handling regular shipments, bulk desiccant packs offer consistent supply and better cost control.

Together, these formats form complete shipping container moisture solutions that can be tailored to different industries, from textiles and leather to electronics, pharmaceuticals and agricultural exports.

Final Thoughts

Moisture damage is predictable, and therefore preventable. Measure your container volume, understand your cargo, consider the route, and choose a desiccant quantity that leaves a margin of safety. Doing so protects your goods, your reputation and your margins on every voyage.

If you are unsure about the right dose for your next shipment, share your container type and cargo details with us to get a recommendation tailored to your export needs.