Desiccant Sizing Calculator
Short answer: the desiccant a pack needs is set by water ingress, not product size. Multiply the barrier WVTR in g/m2/day by the pack area in m2, by 30.4, by the shelf life in months. That gives the grams of water to absorb. Divide by the desiccant capacity at your target humidity: ATMOSIScience fiber desiccant holds over 10% of its own weight at 20% RH, over 35% at 50% RH and over 70% at 90% RH, against about 30% for common silica gel at 90% RH.
Enter your pack figures and the calculator returns the fiber desiccant mass, the silica gel equivalent and a suggested format.
Indicative published ranges. Film WVTR is rated at 38 C and 90% RH, a deliberate worst case, so the result below errs on the safe side. Confirm the real figure with your film supplier.
A 200 x 300 mm flat pouch has about 1200 cm2 of surface across both faces. A 1 litre bottle is roughly 500 to 600 cm2.
Capacity figures come from the ATMOSIScience fiber desiccant technical criteria: over 10% of own weight at 20% RH, over 35% at 50% RH, over 70% at 90% RH.
Fiber desiccant needed
0 g per pack
Silica gel equivalent uses the conservative 2.5 to 1 ratio published in the Fiber Desimat specification table. Treat this as a first-pass estimate, not a validated specification.
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Send this to our engineers and get the real specification
We run the full JEDEC J-STD-033B.1 calculation against your actual pack, recommend the format, and send the document pack: MSDS, SGS recyclability report, ISO 14067 carbon footprint, RoHS and the EN 13432 compostability test basis. Accelerated shelf-life testing is available if your QA file needs measured data.
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How the calculation works
Desiccant is sized against water ingress, not against product weight. Over a shelf life of M months, the water that crosses the barrier is the permeation rate multiplied by the exposed area and the time:
water (g) = WVTR (g/m2/day) x area (m2) x 30.4 x months
That water has to be held by the desiccant without the internal humidity rising past your target. Divide the water by the desiccant capacity at that humidity and you get the mass required. The same logic underpins the desiccant quantity calculation in IPC/JEDEC J-STD-033, which expresses the result in desiccant units rather than grams.
Capacity figures used
| Relative humidity | ATMOSIScience fiber desiccant | Common silica gel |
|---|---|---|
| 20% RH | Over 10% of own weight | Lower at this band |
| 50% RH | Over 35% of own weight | Lower at this band |
| 90% RH, 25 C | Over 70% of own weight, saturating above 100% | About 30% of own weight |
Source: ATMOSIScience fiber bagged desiccant and Fiber Desimat product specifications.
Why the answer is usually less material than you expect
A fiber desiccant holds two to three times the water of the same mass of silica gel, so the pack carries less material, less weight and less packaging fee. The published Fiber Desimat equivalence table puts a 0.15 g card against 0.5 g of silica gel, a 0.35 g card against 1 g, and a 1.0 g card against 2.5 g.
Where the estimate stops and testing starts
This calculator assumes a sealed pack, a steady external humidity and a barrier whose WVTR you have measured. Real packs leak at seals and closures, open and close in use, and travel through changing climates. For anything going into a QA file, ask us for the JEDEC calculation on your drawing and, where it matters, accelerated shelf-life testing on the finished pack.
Related reading
How much desiccant per package · Desiccant units, MIL-D-3464 and JEDEC · Silica gel equivalency in grams · Paper desiccant explained · Sheets, rolls or die-cut cards · Fiber desiccant for B2B · Request a sample pack