Australia Post Shipping Guide: When to Use Flat Rate Satchels vs Your Own Packaging

Introduction: The Australian Shipping Challenge

Shipping products across Australia presents a unique logistical challenge. The vast geography means that sending a package from Sydney to Perth can be as expensive as shipping it internationally. To combat this, Australia Post introduced the 'If It Packs, It Posts' flat-rate National Satchels. But are they always the cheapest option for e-commerce sellers?

The right choice depends on the satchel size, packed dimensions, weight, service, destination and the current quote. This guide separates prepaid satchels from your own packaging so you can compare a real packed item instead of relying on a universal cheapest option.

Understanding 'If It Packs, It Posts' Satchels

Australia Post's current product range includes several prepaid satchel sizes. Check the live product page for the available size, packed dimensions, price, weight limit and service terms because ranges and prices can change.

• Small (35.5 x 22.5 cm): ~10.95 AUD Medium (38.5 x 26.5 cm): ~14.80 AUD Large (40.5 x 31.0 cm): ~18.65 AUD Extra Large (51.0 x 43.5 cm): ~22.45 AUD

Prepaid satchels bundle packaging and postage under the product's current terms. Own packaging is quoted differently and can depend on packed size, weight, destination and booking channel. Compare the same packed item using a current Australia Post quote rather than treating an old example price as a promise.

When to Use Your Own Packaging

If flat-rate satchels are so great, why would you ever use your own boxes? The answer lies in the base rates for light items and local delivery zones.

With your own packaging, Australia Post calculates the applicable service using the packed dimensions, weight, destination and booking channel. A light item may be cheaper in one route and not another, so use a current quote instead of assuming local or interstate pricing.

• Lightweight Items (Under 1kg): If it's going locally, own packaging is usually cheaper. Bulky but Light Items: A large plush toy might weigh only 600g but require an Extra Large satchel ($22.45). Depending on the volumetric weight, shipping it in a custom box locally might only cost $15.00. Branding: Own packaging allows for custom branded boxes, which enhances the unboxing experience—a critical factor for premium brands.

The Volumetric Weight Trap (Cubing)

When using your own packaging, you must be aware of 'cubing' or volumetric weight. Australia Post uses a volumetric divisor of 4000 (Length x Width x Height in cm / 4000 = equivalent kg). If you ship a very large, light box, they will charge you based on the volumetric weight, not the actual scale weight. Flat-rate satchels do not have volumetric weight penalties—if it fits, it posts!

How Our Free AusPost Optimizer Can Help You

Manually calculating volumetric weight, checking local zone base rates, and comparing them against the 4 satchel sizes for every order is impossible at scale. That is why we built the free Australia Post Satchel Optimizer.

Simply enter your item's dimensions, weight, and destination zone. The tool instantly calculates the volumetric weight, checks if it physically fits inside one of the flat-rate satchels, and provides a direct cost comparison, telling you exactly which method saves you the most money.

Conclusion: Mix and Match for Maximum Margin

A practical workflow is to measure and weigh a packed sample, check that it fits without bulging, compare a prepaid satchel with an own-packaging quote, and record the service and date used. Recheck the comparison when Australia Post changes its product range or prices.