I ship posters in cylinder tubes and clothes in soft mailer bags: how do I measure those for volumetric weight?
Treat an irregular parcel as the smallest box it would fit in: a tube is its length × diameter × diameter, and a soft bag is its length, width and thickness at the fullest point once packed. That is how carriers usually do it, and since the calculator assumes a rectangular box, those three extreme dimensions are what it needs from you.
Tubes: why the diameter counts twice
A cylinder takes up a square cross-section on a shelf or in a container, because the space around it cannot really be used. So it is measured like a box whose width and height both equal the tube's diameter. Measure the diameter across the outside of the end cap, which is often wider than the tube body.
- A poster tube 90 cm long, 10 cm across, weighing 1.2 kg: enter 90 × 10 × 10 and the volumetric weight is 1.8 kg with 5000 as an example divisor, which applies.
- That 1.8 is about half as much again as the actual weight. Long light tubes lose out here, so pick the shortest tube that fits the rolled print.
Soft bags: measure them full, not flat
A poly mailer is flat when empty, but it swells once the clothes go in. The packed thickness is what matters, and it is what the courier's staff will measure. Two results for the same bag, again with 5000 as an example:
- A 40 × 30 cm bag, 8 cm thick once packed, weighing 0.9 kg: volumetric weight 1.92 kg.
- The same bag stuffed until it is 12 cm thick: volumetric weight 2.88 kg.
Four extra centimetres of thickness added nearly a full kilo of chargeable weight. Folding tightly and pressing the air out before sealing saves you more here than anything else.
Measuring step by step
- Put the parcel on a flat surface in its final packing.
- Measure the longest side, then the widest, then the highest point, without squashing the bag by hand while you measure.
- Enter the three numbers in the Volumetric shipping-weight calculator with the actual weight and the divisor your carrier gives you.
- If you are sending several parcels of that same size, put the count in Identical packages.
Limits of this approach
This is a working rule, not an official one. Some carriers add special charges for irregular or non-stackable parcels, which the tool knows nothing about, so your carrier's rules come first. If you want a record of the parcel's shape in case of a dispute, photograph it beside a tape measure and crop the picture so the reading is clear with the Image cropper.
Common questions
Should I use the formula for the volume of a cylinder?
Not for volumetric weight. Carriers usually measure the extreme dimensions, and the true cylinder volume is smaller than the box around it.
What about a parcel with something sticking out on one side?
Measure to the tip of it, because it is part of the longest dimension.
Are bags always cheaper to ship than cartons?
Not always. A stuffed bag can reach the weight of a small carton, so run both.