ParcelFitInside for fit. Outside for postage.
A box’s listed size may be internal. Check the usable space for your item, then measure the closed package for postage.
Free Australian packaging calculator
The right box.
Less postage guesswork.
Find a box that fits, understand cubic weight, and head to Australia Post with the measurements you need.
No account neededYour measurements stay hereFree to use
New to sending parcels? How ParcelFit works
- Measure: the item if you need a box, or the outside of your sealed parcel if it is packed.
- Add weight: estimate the item + box + packing materials, or weigh the sealed parcel. You can skip the estimate when finding a box.
- Compare: find a box that fits and see how its size affects the weight used for planning.
- Confirm: measure and weigh the finished parcel, then check postage costs with Australia Post.
02Your box & weight guide
Planning estimateThese rules were checked more than 90 days ago. Confirm the latest guidance with Australia Post.
Enter your measurements, then calculate to see your result.
Estimated physical weight
Cubic weight Weight based on box size
Higher weight for planning
Where cubic-weight pricing applies, Australia Post may use the greater of actual and cubic weight. This is not a postage price.
What is cubic weight?
Shipping companies sometimes work out a parcel’s weight from how much space its box takes up. This is called cubic weight. A bigger box can cost more to send, even when the contents are light.
Same actual weight, different box sizes: both parcels below weigh 1 kg on the scales. Measurements are outside dimensions.
Smaller box20 × 20 × 20 cmCubic weight: 2 kg
Bigger box40 × 30 × 20 cmCubic weight: 6 kg
The higher weights for planning are 2 kg and 6 kg when this pricing method applies. These are worked examples, not box recommendations or promised savings. Eligible Australia Post flat rate packaging at 5 kg or under uses size-based pricing instead.
See the formula and official sourcesCompare box options
These are box designs, not products for sale. Weight figures are estimates, not prices.
How these results are worked out
Postage and packaging costs: not quoted. No verified dollar prices.
Enter your final packed measurements on Australia Post.
Using eligible Australia Post flat rate packaging at 5 kg or under? Size-based pricing may apply instead. Check the official options; we do not verify satchel fit.
Did this help you choose packaging?
Small measurements. Better decisions.
Give your item some breathing room.
Clearance is added on both sides of every dimension. Choose protection for the item; a tighter box is only useful if it still protects it.
Light doesn’t always mean small.
Cubic weight accounts for the space your parcel takes up. Reducing excess box volume can reduce this weight, but doesn’t guarantee a lower price.
Australia Post domestic guidance checked 21 October 2026.
Independent tool. No carrier affiliation or guaranteed service eligibility.How it works & sources →
Independent tool. No carrier affiliation or guaranteed service eligibility.How it works & sources →