How many gel packs do you need? Complete calculation formula
Short answer: for a 24-hour shipment at 15 to 20 °C, count on roughly 200 grams of gel packs per kilo of product (formula: product weight × 0.2). For 48 hours of transport in summer, that rises to roughly 500 grams per kilo. Also correct for transport time, outside temperature and the type of box. The exact factors are given below.
A shortage of coolant means a risk of spoilage, an excess means unnecessary shipping costs and weight. With this calculation formula you determine the right amount. Treat the result as a starting point: the actual performance depends on your box, filling and route.
The basic formula
For a typical 24-hour shipment at normal outside temperatures (15 to 20 °C):
Gel packs needed (grams) = Product weight (grams) × 0.2
So: 5 kg of meat × 0.2 = 1 kg of gel packs (e.g. 2 or 3 packs of 400 g)
Adjustment factors
Transport time
- 12 hours: multiply by 0.5
- 24 hours: standard (1.0)
- 48 hours: multiply by 1.8
- 72 hours: multiply by 2.5
Outside temperature
- Winter (0 to 10 °C): multiply by 0.7
- Spring/autumn (15 to 20 °C): standard (1.0)
- Summer (20 to 25 °C): multiply by 1.4
- Hot summer (25 °C or more): multiply by 1.8
Insulation of the box
- EPS box 30 mm wall: standard (1.0)
- EPS box 50 mm wall: multiply by 0.7
- Honeycomb box: multiply by 1.2
- Standard cardboard box: multiply by 2.5
Example calculation
You ship 3 kg of fish, 48 hours of transport, summer (24 °C), EPS box with 30 mm wall:
3000 g × 0.2 = 600 g base
600 × 1.8 (48 hours) = 1080 g
1080 × 1.4 (summer) = 1512 g
Result: roughly 1.5 kg of gel packs needed. That is, for example, 4 packs of 400 g.
Second example: winter, thick wall
You ship 10 kg of product, 24 hours of transport, winter, EPS box with 50 mm wall:
10000 g × 0.2 = 2000 g base
2000 × 1.0 (24 hours) = 2000 g
2000 × 0.7 (winter) = 1400 g
1400 × 0.7 (50 mm wall) = 980 g
Result: roughly 1 kg of gel packs. That is, for example, 3 packs of 400 g. The difference from the first example shows how much a thick wall and a cold period gain you.
Applying it step by step
- Weigh the product including inner packaging and calculate in grams.
- Determine the transport time and include the waiting time. Calculate with the longest realistic duration, not the best.
- Choose the outside temperature of the warmest day in your shipping period.
- Choose the box and the factor for the insulation. See also choosing the right box size.
- Multiply and round up to whole packs.
- Check with a measurement on your first shipments.
When do you depart from the formula?
The formula is an average. If you are dealing with a shipment with a lot of empty space, a very sensitive product or a route with uncertain waiting times, extra margin is sensible. If your route is short and fixed, and you have measurements that show ample margin, you may be able to save packs. Decide that on the basis of your own measurement data, not on gut feeling. A small change each time and a new measurement is safer than one big leap.
Pro tips
- Distribute the gel packs around the product, not only on one side
- Place on top of the product (cold sinks) for fresh products
- Always use absorbent pads to catch meltwater
- Pre-freeze the gel packs for at least 24 hours. You can read more about this in freezing and packing ice packs.
- Test your packaging with a data logger if in doubt
Common mistakes in the calculation
- Counting the weight of the box. The formula starts from the product weight.
- Calculating only the trip. Loading, unloading and waiting for the courier count towards the transport time.
- Not adjusting per season. A set-up for March is too light for August.
- Taking a box that is too large. A lot of air in the box means more coolant for the same result.
- Using packs that have not been pre-frozen. A pack that is not fully frozen delivers less cooling.
Table: quick reference
| Product weight | 24h (standard) | 48h (summer) |
|---|---|---|
| 1 kg | 200 g | 500 g |
| 2 kg | 400 g | 1000 g |
| 5 kg | 1000 g | 2500 g |
| 10 kg | 2000 g | 5000 g |
Frequently asked questions
Does the formula also apply to frozen goods?
The formula is intended for chilled shipments. For frozen goods, insulation is even more important. Contact us for advice for your situation.
What if my result does not come out at whole packs?
Round up. Better one pack too many than a shortage. Do watch the total weight of the shipment.
What is the difference between gel packs and a rigid cooling element?
That difference determines how you place them and how long you pre-freeze. Read rigid cooling element or gel pack.
Still in doubt?
For specific calculations for your use case, you can contact our sales support team. We have experience with thousands of customer situations and are happy to help.
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