Air volume sets the baseline
20ft, 40ft, and 40ft high-cube hold different air volumes, and cartons, shrink wrap, or loose stow change how much of that air the desiccant must dry.
Container desiccant calculator.
Container rain is condensation: the air and cargo inside a loaded container carry water, and when the steel cools past the dew point at sea, that water films on the ceiling and drips back onto the top tiers. A container desiccant calculator sizes the kilograms of desiccant needed to absorb that moisture load before it condenses.
Adjust for container size, cargo type, packaging, pallets, transit days, and route humidity - and see the full moisture-load math behind every number.
Free buyer tool
Container Desiccant Calculator
Estimate the desiccant kg your container needs from its size, cargo, packaging, pallets, transit time, and route climate - with the full formula shown, not a black box.
4kg desiccant
Recommended format: 1 kg container desiccant strips - 4 × 1 kg for a 40ft standard container (121 DIN 55473 units equivalent). Hang strips evenly along the ceiling line and upper corrugations.
Estimated moisture load to control: ~1.09 litres of water over 25 days.
Moderate risk
Typical export exposure - dose to the recommendation and distribute strips evenly along the ceiling.
Show the math
Formula: desiccant kg = [ (Vair × AH) + (0.6% × V × AH × days) ] × cargo factor × wood factor ÷ 300 g/kg
- Trapped air moisture. Air at 26°C and 75% RH holds 18.2 g of water per m³ (Magnus saturation formula). Free air volume = 67.7 m³ × 0.65 packaging factor = 44 m³ → 802 g of water sealed in at loading.
- Air leakage over the voyage. A sound dry box exchanges ~0.6% of its air volume per day through the door seals: 0.006 × 67.7 m³ × 18.2 g/m³ × 25 days = 185 g.
- Cargo moisture. Some components (pallets, corrugated, fillers) release moisture into the container air. Factor: ×1.1.
- Pallet / wood moisture. Plastic pallets, slip sheets, or floor-loaded cargo add no wood moisture. Factor: ×1 → total load 1,085 g (~1.09 litres).
- Desiccant sizing. Container-grade silica gel adsorbs up to one-third of its weight in water vapor; we size at a 300 g/kg working capacity for margin: 1,085 g ÷ 300 g/kg = 3.62 kg, rounded up to 4 kg (4 × 1 kg strips). DIN 55473 cross-reference: ≈ 121 units at ~33 g silica gel per unit.
Calibrated to DryGelWorld's published loading guidance: ~1.5-3 kg per 20ft and ~3-6 kg per 40ft depending on route length, humidity, and cargo risk. Undried pallet wood and very long tropical voyages can push past the top of the band - when they do, trust the per-shipment estimate, not the band.
Estimate for planning only. Final allocation depends on exact cargo moisture content, container condition, and seasonal route conditions - the DryGelWorld export desk confirms your dosage with the quote.
How this calculator works.
The calculator estimates the grams of water your container must control, then sizes the desiccant against silica gel's working capacity. Three moisture sources are added together: the water vapor sealed into the container's free air at loading (container volume × packaging air factor × absolute humidity), humid air leaking through the door seals over the voyage (about 0.6% of the container volume per day), and moisture released by hygroscopic cargo and wooden pallets or dunnage (multipliers of up to 1.2× and 1.15× respectively). The total is divided by 300 g of water per kg of silica gel - a working capacity below the "one-third of its own weight" maximum, so the recommendation keeps a safety margin - and rounded up to the next half kilogram.
The output is calibrated to DryGelWorld's published loading guidance: roughly 1.5-3 kg per 20ft container and 3-6 kg per 40ft container depending on route length, humidity, and cargo risk, delivered as 1 kg or 2 kg strips hung at the ceiling line.
| Parameter | Value used | Basis |
|---|---|---|
| Container air volumes | 20ft standard ~33.2 m³ · 40ft standard ~67.7 m³ · 40ft high-cube ~76.4 m³ | Standard internal capacities for ISO dry boxes. |
| Free-air fraction by packaging | Cartons on pallets 65% · Shrink-wrapped pallets 55% · Loose / unpackaged 75% | Share of container volume behaving as exchangeable air around the stow. |
| Route climate presets | Dry / temperate 60% RH / 20°C · Mixed / seasonal 75% RH / 26°C · Tropical / humid 85% RH / 30°C | Typical loading-season conditions; both values are user-adjustable. |
| Absolute humidity | Magnus saturation formula × RH | Air at 30°C / 80% RH holds ~24 g of water per m³ - a loaded 40ft box seals in close to 1.5 kg. |
| Daily air exchange | 0.6% of container volume per day | Effective leakage of a sound, sealed dry box through door gaskets; scales the load with transit days. |
| Cargo moisture factor | Non-hygroscopic ×1 · Mixed cargo ×1.1 · Hygroscopic ×1.2 | Hygroscopic cargo (textiles, leather, paper, wood, food) releases moisture as temperature cycles. |
| Pallet / wood factor | No pallets or wood dunnage ×1 · Kiln-dried pallets ×1.05 · Air-dried, HT-only, or unknown-moisture wood ×1.15 | Pallets and dunnage carry their own moisture into the box; undried wood is a major hidden source. Planning multipliers, not laboratory measurements. |
| Silica gel working capacity | 300 g of water per kg | Container-grade silica gel adsorbs up to one-third of its weight; 30% is the design value for safety margin. |
| Rounding | Rounded up to the nearest 0.5 kg, minimum 1 kg | Under-rounding a dosage under-protects the cargo; always round up. |
What moves the dosage.
The same factors our export desk uses to right-size a container desiccant program.
Humidity and days at sea
Longer, tropical, cross-equator routes cycle through more condensation events and admit more humid air through the door seals - both scale the load.
Hygroscopic cargo adds moisture
Textiles, leather, paper, wood, and food carry their own moisture and release it as temperature cycles, so they need a higher allocation than metal or plastic goods.
Container desiccant FAQ.
How much desiccant do I need for a 20ft container?
As a planning baseline, a 20ft container needs roughly 1.5-2 kg of container-grade desiccant for low-risk industrial cargo on a ~20-day route, rising to about 3 kg plus carton-level sachets for high-risk cargo such as leather or electronics on humid routes. The calculator adjusts within that band using transit days, route humidity, cargo type, and packaging.
How much desiccant for a 40ft container?
Around 3-4 kg for low-risk cargo on a 25-30 day route, and 5-6 kg for high-risk or hygroscopic cargo on 30+ day tropical routes. A 40ft high-cube sits slightly higher because of its extra air volume (~76 m3 versus ~68 m3). Voyages beyond about 50 days need sealed liners on top of desiccant.
How does this calculator estimate the moisture load?
It computes the water vapor sealed into the container's free air at loading (volume x packaging air factor x absolute humidity from temperature and RH), adds daily humid-air leakage through the door seals over the voyage (~0.6% of container volume per day), applies factors for moisture-releasing cargo and for pallet/dunnage wood, and divides the total grams of water by silica gel's ~300 g/kg working capacity to get desiccant kg.
Do wooden pallets change how much desiccant I need?
Yes. Wood carries its own moisture into the sealed container and releases it as the box heats - undried pallets and dunnage are the classic cause of container rain on loads that were otherwise dry. The calculator applies a planning surcharge for verified kiln-dried pallets and a larger one for air-dried, HT-only, or unknown-moisture wood; plastic pallets or floor-loaded cargo add nothing. Note that an ISPM 15 'HT' stamp certifies heat treatment against pests, not dryness.
Which format should I use - hanging strips, bags, or sachets?
Hanging strips at the container ceiling are the default for container-level protection because condensation forms at the roof. Bulk desiccant bags suit doses above ~10 kg or floor placement between pallets. Carton-level sachets are an addition, not a substitute: they protect individual boxes on high-risk or hygroscopic cargo while strips handle the container air. The calculator recommends strips first and flags when sachets or liners should be added.
Where should container desiccant strips be placed?
Hang strips evenly along the container ceiling and upper corrugations so the desiccant sits above the cargo where condensation forms. Even distribution outperforms concentrated placement.
How do desiccant kilograms convert to DIN 55473 units?
One DIN 55473 unit corresponds to roughly 33 g of silica gel, so 1 kg is about 30 units and a 4 kg container dose is about 120 units. If your buyer's specification is written in units, convert to grams at ~33 g per unit first, then size the strip count - and confirm the quoted units are true DIN 55473 units.
Is this calculator a guaranteed dosage?
No - it is an estimate for planning. Final allocation depends on exact cargo moisture content, packaging barrier, container condition, and seasonal conditions. DryGelWorld confirms your dosage when preparing the quote.
Next steps.
Move from estimate to a confirmed export quote.
Supply
Shipping container desiccant supplier
Formats, strip options, and export supply for sealed ocean freight.
GuideContainer rain prevention
How condensation forms inside containers and how to stop it - with the sizing bands this calculator is anchored to.
GuideDesiccant quantity guide
The full buyer walkthrough behind this tool - formats, placement, and what an export quotation needs.
GuideDIN 55473 desiccant units
Converting unit-based container specs into silica gel grams and strip counts.
PricingDesiccant pricing
Format-by-format price guidance for sachets, strips, and bulk supply.
RFQRequest an export quote
Send your container size, route, and cargo for a confirmed dosage and price.