Australia Post Shipping Guide: When to Use Flat Rate Satchels...

Learn how to optimize your Australia Post shipping costs in 2026. Compare the If It Packs, It Posts National Satchels against 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 short answer is no. While flat-rate satchels offer incredible value for heavy, dense items traveling interstate, they can be an expensive mistake for light items traveling locally. In this guide, we will break down exactly when you should use Australia Post satchels versus when you should pack items in your own custom boxes.

Understanding 'If It Packs, It Posts' Satchels

Australia Post offers four main sizes of prepaid or flat-rate satchels: Small, Medium, Large, and Extra Large. The revolutionary feature of these satchels is the weight limit: they all allow up to 5kg.

• **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

Because the price is fixed regardless of destination within Australia, these satchels are incredibly powerful for cross-country shipping. If you can fit 4kg of dense material (like books or cosmetics) into a Small satchel, you can ship it from Melbourne to Darwin for just $10.95. Using your own packaging for a 4kg interstate parcel would easily cost over $25.00.

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.

When you use your own packaging, Australia Post calculates the price based on weight and distance (Local, Same State, or Interstate). If you are shipping a very light item (under 500g) locally within the same city, the base rate for your own packaging is often cheaper than even the Small satchel.

• **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!

The Satchel Stretch Limit: While you can technically 'stretch' a poly satchel around a bulky item, be careful. If the satchel is altered, torn, or stretched to the point where it exceeds maximum allowable dimensions, Australia Post may reject it or charge an underpaid postage fee.

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

The most profitable Australian e-commerce sellers do not rely on a single shipping method. They stock a mix of Australia Post flat-rate satchels for dense, interstate orders, and custom-branded boxes for light, local deliveries. By intelligently routing your orders to the correct packaging type, you can shave dollars off every shipment and drastically improve your bottom line.

Frequently Asked Questions

• What is the maximum weight limit for Australia Post prepaid satchels?

  Under Australia Post's 'If It Packs, It Posts' national flat-rate scheme, all standard prepaid satchel sizes (Small, Medium, Large, and Extra Large) support a maximum weight limit of up to 5 kg for deliveries within Australia.

• What are the dimensions for Australia Post Small, Medium, Large, and XL satchels?

  Approximate satchel dimensions are Small (355 x 225 mm), Medium (405 x 310 mm), Large (435 x 315 mm), and Extra Large (510 x 440 mm). Items must fit inside the satchel without bulging so the self-adhesive seal closes completely.

• When does Australia Post apply cubic weight charges instead of flat-rate satchel pricing?

  Cubic weight charges apply to oversized cartons and non-standard packaging when volumetric weight (Length x Width x Height in meters multiplied by 250) exceeds dead weight. Using standard satchels protects sellers from cubic freight penalties.

• Can I print Australia Post shipping labels directly on a 4x6 direct thermal printer?

  Yes. Australia Post MyPost Business and ParcelSend generate standardized 4x6 inch (100x150 mm) labels formatted for direct thermal printers like Zebra, Brother, and Rollo at 203 DPI resolution.