How big can my box get before volumetric weight overtakes the actual weight of a 3 kg order?
The two weights are equal when the volume divided by the divisor equals the actual weight. So the largest volume is actual weight × divisor. For a 3 kg order with 5000 as an example divisor: 3 × 5000 = 15,000 cm³. Any carton bigger than that makes the volumetric weight the one that applies.
Testing the threshold in the tool
I tried three cartons for a 3 kg order, with 5000 as an example divisor:
- 25 × 25 × 20 cm (12,500 cm³): volumetric weight 2.5 kg, so the actual 3 kg applies.
- 30 × 25 × 20 cm (15,000 cm³): volumetric weight exactly 3 kg, and the tool says Both are equal.
- 35 × 25 × 20 cm (17,500 cm³): volumetric weight 3.5 kg, so volumetric now applies.
Five centimetres on one side moved the parcel from actual-weight territory into volume territory. The divisor moves the line: with 6000 as an example it becomes 3 × 6000 = 18,000 cm³, and the 30 × 25 × 20 cm carton gives a volumetric weight of just 2.5 kg, so the actual weight applies.
Why the threshold matters when you buy cartons
Buying cartons in bulk means choosing sizes you will use for months. If you know what your orders typically weigh, you can work out for each size the lowest weight that keeps it safe. A 15,000 cm³ carton suits orders of 3 kg or more with that divisor, while a 1 kg order has a limit of only 5,000 cm³.
- List your usual packed order weights, even roughly.
- Multiply each by the divisor your carrier gives you to get the largest volume.
- Test candidate sizes in the Volumetric shipping-weight calculator: if volumetric weight applies, the carton is too big for that weight.
- Choose two or three sizes that cover most orders without going far past the line.
Is crossing the line always a loss?
Not necessarily. Going slightly over may not change the price if the chargeable weight stays in the same band on your carrier's table, and the tool knows nothing about those bands. A fragile product also needs room for protection even if it costs half a kilo extra. The threshold helps you decide; it is not a rule to follow blindly.
If a product cannot avoid crossing it, put the chargeable weight into its shipping cost and price it with the Selling-price calculator. Record the approved carton for each product on your packing list with the Packing-list generator, so nobody grabs a bigger box.
Common questions
Is it the same formula in inches and pounds?
Yes: largest volume in in³ = actual weight in lb × the divisor in in³ per lb.
What does Both are equal mean?
The chargeable weight is the same figure either way, and you are exactly on the line.
Does the tool calculate the threshold for me?
There is no threshold field, but you test it by entering sizes and watching Weight that applies.