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Which weight will the carrier charge?
Volume divided by the carrier divisor gives dimensional weight. Carriers bill the greater of that and the scale weight.
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The divisor is the whole calculation
Dimensional weight is length times width times height divided by a carrier divisor. The divisor encodes how much space the carrier assumes one pound occupies; a lower divisor produces a higher billable weight. US domestic parcel rates commonly use 139, some services use 166, and metric carriers often use 5000 with centimetres and kilograms.
The calculator compares the dimensional result with the actual scale weight and reports the larger value. That is the billable weight, not necessarily the weight you would measure on a scale.
Why a light box can cost more than a heavy one
Large, low-density items are priced on the space they take. A 12 x 9 x 6 inch box at a divisor of 139 is about 4.7 pounds dimensional weight; if the item weighs 2 pounds, the carrier bills 4.7. Reducing one dimension or switching to a mailer can move the billable weight below the actual weight and take the dimensional penalty out of the rate.
The volume output helps compare packaging options directly: the ratio of dimensional to actual weight shows how much air you are shipping.
Using it before you buy packaging
Measure the outer carton, not the product. Run the two candidate box sizes and compare billable weight; the smaller box wins even when its material cost is slightly higher. Recheck after the first carrier invoice, because the divisor on your negotiated rate card may differ from the public one.
Round dimensions up to the nearest inch or centimetre the way the carrier measures them; the calculator does not round input for you.
Frequently asked questions
Which divisor should I use?
Use the divisor printed on your carrier rate card. 139 is common for US domestic parcel services, 166 for some retail services, and 5000 for centimetre/kilogram markets.
Does the calculator round the dimensional weight?
It rounds to one decimal place for display. Carriers may round up to the next whole pound; treat the result as a close estimate.
Does it work in centimetres?
Yes, if you enter centimetres and use a metric divisor such as 5000. Do not mix inches with a metric divisor.
Is dimensional weight used for every parcel?
Most parcel services apply it above a size threshold. Check the specific service; some small or flat-rate services use actual weight only.