How to calculate cubic weight

What is cubic weight?

Also known as dimensional weight, cubic weight is a way of calculating the weight of a package by its size rather than its actual weight. 

This is because shipping companies need to account for the amount of space that a package takes up in a vehicle, as well as its weight, when calculating the cost of shipping.

When calculating the cost of shipping Australia Post typically uses the greater of a package's cubic weight or actual weight.

A great way to remove any uncertainty about chargeable weight is to use an Australia Post pre-paid satchel or flat rate packaging range.

How to calculate cubic weight in kg

Cubic weight in kilograms is calculated by measuring and multiplying the length, height and width of a parcel in metres, and then multiplying the result by a cubic weight conversion factor. At Australia Post, we use a cubic conversion factor of 250kg per cubic metre. 

To calculate the cubic weight of a parcel that measures 50cm long, 30cm high and 40cm wide: 

(0.5m) × (0.3m) × (0.4m) = 0.06m × 250 = 15kg

When is cubic weight used to calculate shipping fees?

Where you use your own packaging or any other packaging which is not eligible for the national flat rates for postage based on size, Australia Post will assess charges according to their actual weight or cubed weight equivalent, whichever is greater. 

For example, if a parcel weighs 10kg but has a cubic weight of 15kg, Australia Post will calculate shipping charges using the cubic weight.

For parcels lodged under non-contract conditions (for example through My Post Business Australia Post will generally not apply cubic charging to parcels weighing less than 1kg actual weight, although we reserve the right to also apply cubic charges to a parcel weighing less than 1kg, and this will be more likely in instances where a parcel is large in size, or irregular or cylindrical in shape.

How to work out cubic weight of an irregularly shaped parcel

If your parcel is a cylinder, satchel or other oddly shaped object, then you’ll need to use the maximum point for each of the length, height and width to calculate the cubic weight.

Does Australia Post have a cubic weight calculator?

Using Australia Post’s postage calculator, you can enter the dimensions and weight of your parcel to determine the cost of shipping. 

Find our handy postage calculator here.