Start with box volume, not guesswork
The number of desiccant packets per box is a calculation, not a habit. Begin with the box's internal volume in cubic meters (length × width × height in meters). Most product cartons fall between 0.01 and 0.1 m³. The baseline rule DryGelWorld uses: a sealed carton at average export humidity holds roughly its volume × 20 g of water vapor, and you provide silica gel at about 3× that — volume × 60 g — as the starting dose. Once you have the gram target, the packet count is simply the gram target divided by your chosen packet size, rounded up. Everything else (route, barrier, storage) adjusts that baseline up or down.
- Internal volume V (m³) = length × width × height in meters.
- Baseline water load ≈ V × 20 g; baseline silica gel ≈ V × 60 g.
- Packet count = gram target ÷ packet size, rounded up.
- Adjust the baseline for route, barrier quality, and storage time.
Worked example: a standard export carton
Take a 0.4 m × 0.3 m × 0.25 m carton = 0.03 m³. Baseline silica gel = 0.03 × 60 g = 1.8 g. With 1 g packets you would use 2; with a single 2 g packet, one. Now apply route: a tropical-to-temperate 25-day voyage adds 50–100%, so multiply by ~1.75 → ~3.2 g, i.e. one 5 g packet or three 1 g packets. If the carton is multi-walled corrugated with a good liner (a decent barrier) keep it there; if it is a vented or loosely sealed box, add margin. The point of the worked example is that the same carton can honestly need anywhere from 2 g (short route, sealed) to 5 g+ (long humid route, weak barrier) — and the math tells you which.
- 0.03 m³ carton → baseline 1.8 g.
- 25-day tropical route (×~1.75) → ~3.2 g → one 5 g packet.
- Good liner/barrier: hold the figure; vented box: add margin.
- Same carton ranges 2 g–5 g+ depending on route and barrier — the math decides.
Adjust for the packaging barrier
The desiccant only has to fight the water that gets in. A near-hermetic barrier (foil laminate, sealed moisture-barrier bag) means little new water enters, so you size for the trapped air plus goods moisture and can stay near baseline. A breathable or vented box continuously admits humid air, so the desiccant is fighting the whole voyage's humidity and needs sizing up — sometimes doubling. This is why a moisture-barrier bag (MBB) around electronics dramatically cuts the desiccant needed inside it: the bag does most of the work. Decide the barrier first; it changes the packet count more than almost any other factor.
- Desiccant only fights the water that enters the package.
- Near-hermetic barrier (foil/MBB): size for trapped air + goods moisture, near baseline.
- Breathable/vented box: admits humidity all voyage — size up, sometimes 2×.
- An MBB around the goods can slash the internal desiccant requirement.
- Decide the barrier first — it dominates the packet count.
Add for storage time and stacking
Sizing for the voyage alone under-protects goods that then sit in a destination warehouse for months. Add 30–50% for multi-month storage before the package is opened. Also consider stacking and master cartons: a unit pack inside a master carton inside a pallet has nested micro-environments, so distribute desiccant at the level closest to the goods (unit pack) plus a supplementary dose at master-carton level for long storage. Do not put all the desiccant in the master carton and none in the unit packs — the goods inside each unit pack see their own micro-climate, and that is where damage starts.
- Add 30–50% for multi-month destination storage before opening.
- Nested packaging = nested micro-environments.
- Put desiccant closest to the goods (unit pack), plus supplementary at master-carton level.
- Don't load only the master carton — unit packs have their own micro-climate.
Validate, don't over-pack
Over-packing wastes money and space; under-packing loses cargo. For a serious program, validate before locking the count: pack a representative box with the calculated number of packets, include indicating gel or a humidity card, and run a 14–30 day humidity test simulating the route. If the indicator saturates early, add packets; if it stays fresh at the end, you may be over-packed and can trim 20–30% next order. This converts the calculation into a verified number for that exact product and route, which is worth far more than copying the previous shipment's count.
- Over-packing wastes money/space; under-packing loses cargo.
- Validate: pack the calculated count + an indicator, run a 14–30 day route simulation.
- Saturates early → add packets; fresh at end → trim 20–30% next order.
- A validated count beats inheriting the previous shipment's number.