How much silica gel should I use? Here is how to calculate the correct amount!

How much silica gel do you actually need? That is a question we are asked often – and the answer is not always simple. Too little and your products will rust. Too much is a waste of money. Here we show you how to calculate the correct amount, whether you are packing a small box or filling a 20-foot container.

What is silica gel and why does it work?

Silica gel is a porous desiccant that absorbs moisture from the air via adsorption – no chemical reaction, just mechanical forces. The surface area is enormous – up to 750–800 m²/g – and that makes silica gel the universal desiccant that most people are familiar with. It can absorb more than 30% of its own weight in moisture and lower the relative humidity (RH) to 2% in a closed space. In practice, the goal is to keep RH below 40% – that is when corrosion on metals stops.

Most common is white silica gel, which we stock in bags from 3g up to 2.5kg. Self-indicating silica gel changes color as it becomes saturated with moisture. We stock self-indicating silica gel in 4kg buckets, 12.5kg pails, and 25kg pails.

The formula – how to calculate

The correct amount depends on three things: the packaging area, film type, and storage time. The formula looks like this:

Silica gel [g] = (WTR × A × T) × 5

Where:

• WTR = Water Vapor Transmission Rate (depends on film type)
• A = total area of the packaging walls [m²]
• T = storage or transport time [days]

Common WTR values: plastic 200 μm gives WTR = 0.4. Standard aluminum foil has a significantly lower WTR.

Remember to add the initial moisture content of the goods. For critical applications, we recommend using the DIN 55474 standard.

Use our free silica gel calculator

You don't need to calculate by hand. We have created a simple calculator where you enter packaging dimensions, film type, and transport time – and get the answer in seconds. Use the calculator here.

A practical example: A crate with 6 sides of 1×1 m in 200 μm plastic film, transported for 90 days: (0.4 × 6 × 90) × 5 = 1,080 g of silica gel.

Rule of thumb for containers and warehouses

Need a quick estimate:

• 20-foot container, 90 days sea transport: 16 kg of silica gel
• Equivalent to 0.5 kg per m³ of void space
• A 50-liter cabinet stays dry for 3 months with 25 g of silica gel
• In a dry warehouse you can double the storage time – but always consider how airtight the packaging is

16 kilos of silica for a 20-foot container

Which type of silica gel should you choose?

We stock silica gel bags in all sizes from 3 g to 2,500 g, and self-indicating bulk. Self-indicating silica gel changes color when saturated – convenient for knowing when it is time to replace it. For military and defense-critical applications, we also supply according to MIL-D-3464E Type I and II.

Proper disposal

Used silica gel is normally treated as residual waste – unless it has absorbed hazardous liquids. We always recommend checking local regulations. Read more about how to dispose of used silica gel here!

Unsure about what you need? Call us at 51 94 47 00 or send an email to post@realmarine.no – and we will work it out together.