Australia Post Postage & Parcel Estimator

Australia Post updates rates over time, and parcel pricing can depend on cubic (volumetric) weight. This calculator stays accurate by enforcing stable size/weight math while letting you enter the latest AusPost rate table amounts.

What This Calculator Solves

Australia Post is the default carrier for everyday sending in Australia: letters, documents, and parcels shipped domestically and internationally. The challenge is that postage isn’t a single number. It depends on the format (letter vs parcel), the destination, and the weight band. For parcels, it can also depend on cubic (volumetric) weight—the idea that a light but bulky parcel takes up space in trucks and planes and can be priced as if it were heavier.

If you want a calculator that remains accurate across rate updates, you need to separate two things:

• Rules and math (stable): unit conversions, weight-band rounding, cubic weight calculation, and size-category checks.
• Rate tables (change): the base price and per-band increments for a given service, destination zone, and date.

This tool focuses on the stable part and asks you to input the current rate amounts from Australia Post for your chosen service. That avoids the most common “calculator drift” problem where a tool hardcodes last year’s prices and becomes misleading.

Letters vs Parcels: Two Different Worlds

Australia Post pricing starts with an important split:

• Letters and documents are constrained by strict thickness and dimension limits. A slightly thicker envelope can move from a “small letter” to a “large letter” category.
• Parcels are typically priced by weight (and often cubic weight) plus destination. Dimensions matter for cubic weight and for maximum size limits.

This calculator supports both. For letters, it validates whether your item fits within common “small” and “large” letter limits. For parcels, it optionally computes cubic weight and uses the greater of actual and cubic weight as the billable weight.

Common Australia Post Letter Size Limits (Reference)

Australia Post publishes detailed size standards. The most common retail categories are often described as:

• Small letter (typical): up to 240 mm × 130 mm × 5 mm.
• Large letter (typical): up to 360 mm × 260 mm × 20 mm.

Weight limits and sub-categories can vary by product (domestic vs international, standard vs express). This calculator uses these common dimension checks as a sanity check, not as legal compliance for every product. If your envelope exceeds these limits, you should treat it as a parcel or use a specialized AusPost product category.

Cubic (Volumetric) Weight for Parcels

Cubic weight converts parcel volume into a weight equivalent. For many shipping systems, cubic weight is calculated from parcel dimensions and a divisor. A commonly used divisor in Australian parcel networks is 4,000 when dimensions are in centimeters (cm³ per kg). Some services or international lanes use different divisors, and “dead weight” vs “cubic weight” thresholds can vary. For that reason, this calculator lets you set the divisor explicitly and provides a reasonable default.

Let length, width, and height be measured in centimeters. Cubic weight in kilograms can be computed as:

Billable weight is typically:

Weight Bands and Rate Tables

Australia Post rate tables usually provide prices by weight band (for example: up to 500 g, up to 1 kg, up to 3 kg, etc.) and by destination zone or service. The most reliable way to do arithmetic is to treat the table as “base price for a base band, plus an increment for each additional band.”

This calculator supports a general base-plus-steps model:

• Base band: the weight covered by the base price.
• Step size: the weight per additional band.
• Step price: the additional price per band.

It then rounds up partial bands. This matches the typical “or part thereof” banding logic.

Worked Example (Parcel)

Assume you are shipping a parcel domestically. Your box is 40 cm × 30 cm × 20 cm and weighs 2.2 kg on a scale. Using a divisor of 4,000, cubic weight is (40×30×20)/4000 = 6.0 kg. If cubic weight applies, your billable weight is 6.0 kg, not 2.2 kg.

Suppose the rate table you are using says: base price covers the first 1 kg at $10.00, and each additional 1 kg (or part) costs $2.00. Billable weight 6.0 kg means you have 5 kg beyond the base band, i.e., 5 steps. Total is $10.00 + 5×$2.00 = $20.00 (illustrative).

Now imagine you repack into a smaller box: 30×20×15 cm. Cubic weight becomes (30×20×15)/4000 = 2.25 kg. Billable weight becomes max(2.2, 2.25) = 2.25 kg, which rounds up to 3 kg if the band is 1 kg steps. The smaller box could reduce your billable weight dramatically and lower cost. This is why cubic weight math matters.

Comparison Table: Common Situations

Limitations and Assumptions

This estimator is designed to stay accurate over time by not hardcoding rates. It assumes:

• You enter the correct base price and per-step increment from the current Australia Post table for your service and destination.
• You choose the correct weight step size that matches the table (e.g., per 0.5 kg, per 1 kg, etc.).
• The cubic divisor you use matches the service you’re shipping under (divisors can vary).
• It does not add optional extras (signature, insurance, pickup fees) unless you incorporate them into your rate inputs.

If you need an exact checkout price, confirm in the official Australia Post calculator at the time of purchase. Use this tool to avoid math mistakes, test packaging changes, and compare scenarios quickly.