Practical guide · November 8, 2026
Compare two boxes without mixing assumptions
Keep the service settings constant while changing the package.
Compare complete packed parcels
Measure a safely packed item first. For an alternative box, include its own cushioning and actual package weight. Comparing an empty small box with a fully packed large box understates the trade-off. Do not remove protection solely to make a calculator number smaller.
Work through a size change
At divisor 5000, a 40 × 30 × 20 cm box gives 4.8 kg dimensional weight. A 35 × 25 × 20 cm box gives 3.5 kg. If both weigh 3 kg on a scale, the dimensional estimates differ by 1.3 kg before rounding. This difference is not a guaranteed currency saving.
Keep assumptions fixed
Use the same divisor, unit system and weight increment for both options. Otherwise you are changing the package and the service assumptions simultaneously. Download a text summary for each run to keep the measurements and settings together. For non-identical boxes, compare separate runs rather than using a single quantity.
Check the finished package
Sealing, bulging and protrusions may alter outside dimensions. Ask the carrier how it measures irregular parcels and whether oversize conditions or minimums apply. The tool models a rectangular volume. It does not validate package strength, shipment eligibility, dangerous goods compliance or any carrier's final measurement.