The Truth about Calculating Desiccant
Accurately determining the amount of desiccant needed to properly dehumidify the inside of a rigid storage space can be tricky due to the numerous variables to consider, such as:
- Volume of the air space to be desiccated;
- The material to be protected;
- Moisture surrounding the package;
- Type of desiccant to be used;
- Length of time protection is needed; and
- Atmospheric conditions (temperature and relative humidity) when and where the product is sealed as well as during its subsequent shipment and storage.
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How Does It Work
A general rule of thumb is that 1.2 units of desiccant will protect up to 1 cubic foot (for information about how desiccant units are measured, see here).
As an example, a container measuring 15”x15”x12”, which translates to 2,700 cubic inches or 1.5625 cubic feet, will require 1.9 units of desiccant (1.5625 multiplied by 1.2) to keep dry. However, since not all distributors carry a 1.9-unit bag, it’s recommended to round up – in this case to a 2-unit bag. Generally speaking, it is better to use more desiccant than you need, rather than not enough.
quick-reference guide for desiccating rigid containers
| Rigid Barrier Dimensions | Units Req. | ||
| Cubic Inches | Cubic Feet | Gallons | |
| 237 | 0.14 | 1.1 | 1/6 |
| 476 | 0.28 | 2.1 | 1/3 |
| 715 | 0.42 | 3.2 | 1/2 |
| 1,429 | 0.83 | 6.2 | 1 |
| 2,857 | 1.67 | 12.5 | 2 |
| 4,286 | 2.5 | 18.7 | 3 |
| 5,714 | 3.33 | 25.0 | 4 |
| 7,143 | 4.17 | 31.2 | 5 |
| 8,571 | 5.00 | 37.4 | 6 |
| 10,000 | 5.83 | 43.6 | 7 |
| 11,423 | 6.67 | 50.0 | 8 |
| 12,857 | 7.5 | 56.1 | 9 |
| 14,286 | 8.33 | 62.3 | 10 |
| 17,143 | 10.00 | 74.8 | 12 |
| 20,000 | 11.67 | 87.3 | 14 |
| 22,857 | 13.33 | 99.7 | 16 |
| 28,571 | 16.67 | 125 | 20 |
| 42,857 | 25.00 | 187 | 30 |
| 57,143 | 33.33 | 249 | 40 |
| 71,429 | 41.67 | 309.2 | 50 |
| 85,714 | 50 | 371 | 60 |
| 100,000 | 58.30 | 432.9 | 70 |
| 114,286 | 66.67 | 494.7 | 80 |
A Note about the Example and Guide
The above example and reference guide pertain to rigid containers only, which are defined as moisture-impervious containers made from metal, plastic, glass or combinations of different materials. Furthermore, the above guide does not take into consideration relative humidity (RH) or other on-site atmospheric conditions. As a result, further information is often required to accurately prescribe appropriate desiccant amounts for many shipping and storage containers.
Learn More
For help determining the amount of desiccant that is right for your application, or for information about determining the amount of desiccant needed for non-rigid containers and containers that may be at risk for high moisture vapor transmission, contact AGM at (520) 881-2130, or send us an email.