Australia Post Postage & Parcel Estimator

How this Australia Post postage estimator works

This page helps you estimate Australia Post postage for letters and parcels by combining your own rate table with consistent weight and size calculations. You enter the latest prices from the official Australia Post website or brochures, and the calculator uses those numbers together with either actual weight or cubic (volumetric) weight for parcels.

The tool does not store or fetch any live Australia Post prices. Instead, it focuses on getting the maths right and giving you a repeatable way to apply the same rules to different items.

Key inputs at a glance

• Service type: Choose whether you are sending a letter/document or a parcel.
• Actual weight: Enter the item’s real weight. You can use grams or kilograms.
• Parcel dimensions: Length, width, and height in centimetres, used to work out cubic weight if it applies to your service.
• Cubic weight options: Turn cubic weight on or off and specify the cubic divisor used by your particular Australia Post service.
• Letter dimensions (optional): Length, width, and thickness in millimetres for a basic small vs large letter classification check.
• Rate table fields: Base band weight, base price, additional band size, and price per additional band, copied from your official Australia Post rate table.

Formulas used in the calculator

The calculator uses a small set of simple formulas to keep everything consistent. You can compare these with the rules described on the Australia Post site to confirm they match your service.

1. Converting grams to kilograms

If you enter weight in grams, it is converted to kilograms before any further steps:

2. Parcel cubic (volumetric) weight

Many Australia Post parcel services charge based on the higher of actual weight and cubic (volumetric) weight. The typical cubic weight formula uses centimetres and a divisor published by the carrier:

Here, length, width, and height are in centimetres, and the divisor is in cubic centimetres per kilogram (for example, 4000 cm³/kg). Check the current divisor in your Australia Post service guide and update the field accordingly.

If cubic weight is enabled, the chargeable weight for a parcel is the larger of actual weight and cubic weight. If you disable the cubic option, the calculator uses actual weight only.

3. Band-based price calculation

The rate table section assumes your service uses a base band plus equal additional weight bands. The calculator follows this logic:

1. The base band weight (kg) covers all items up to that weight for the base price.
2. Anything above the base band is split into chunks of the additional band size (kg).
3. Each additional band adds one unit of the price per additional band to the total.

Rounded up to the next full band, this is conceptually similar to:

Total price = base price + (number of extra bands × price per additional band)

Make sure the number of extra bands and rounding behaviour match the way Australia Post calculates for your specific service (domestic vs international, zones, etc.).

How to use the calculator step by step

1. Choose letter or parcel. Use the service selector to indicate what you are sending.
2. Enter actual weight. Weigh your item and enter the value. Pick grams if you have a kitchen scale reading in g, or kilograms if you already converted.
3. For parcels, enter dimensions. Measure length, width, and height in centimetres. These are usually the longest edges of the packed item, not the contents alone.
4. Decide whether to apply cubic weight. Check your Australia Post service description. If it mentions cubic or volumetric weight, switch cubic weight on and set the divisor it specifies.
5. Optional: check letter size classification. If you are sending a letter, you can enter length, width, and thickness in millimetres. The tool can then compare those numbers to common small/large letter boundaries to help you pick the right category.
6. Copy your rate table values. From your Australia Post guide, find the base band weight, the price for that band, the extra weight step, and the price per extra step. Enter those numbers in the rate table inputs.
7. Review the estimated postage. The calculator combines your rate table with the chargeable weight (actual or cubic) to produce an estimate based on the structure you entered.

Interpreting the results

The output is an estimated postage cost based on the bands and prices you supplied. Use it to:

• Compare different packing options (for example, reducing dimensions to lower cubic weight).
• Check whether an item is more cost-effective as a letter or a parcel, if both are allowed.
• Prepare quotes or internal cost estimates that follow the same logic as the official table.

Always treat the result as an approximation. For an official price or to add extra services (tracking, insurance, signature on delivery, surcharges), confirm on the Australia Post website or at a post office counter.

Letter vs parcel: typical use cases

The table below outlines common scenarios and how this calculator fits in. It does not reproduce any official price or proprietary rate values.

Worked example (illustrative only)

Imagine you have a domestic parcel with these details:

• Actual weight: 2.2 kg
• Dimensions: 40 cm × 30 cm × 20 cm
• Cubic divisor: 4000 cm³/kg (example value)
• Base band weight: 1.0 kg
• Base price: AUD 10.00
• Additional band size: 1.0 kg
• Price per additional band: AUD 4.00

The cubic weight is:

Cubic weight = (40 × 30 × 20) / 4000 = 24000 / 4000 = 6.0 kg

Chargeable weight is therefore 6.0 kg (higher than 2.2 kg actual). Up to 1.0 kg is covered by the base band; the remaining 5.0 kg falls into additional bands of 1.0 kg each, so there are 5 extra bands.

The estimated price using the band structure is:

Total price = 10.00 + (5 × 4.00) = 30.00 AUD

This example is purely illustrative. You must replace the divisor, band sizes, and prices with the values from your current Australia Post service.

Limitations, assumptions, and important notes

• Not an official Australia Post calculator: This tool is for guidance only. It is not affiliated with or endorsed by Australia Post.
• User-supplied rate tables: All prices and band structures come from values you enter. Always copy them carefully from the official Australia Post website or printed materials.
• No extra services included: The estimate typically excludes tracking options, insurance, signatures, oversized surcharges, fuel or remote area surcharges, and any temporary fees.
• Domestic vs international differences: Australia Post uses zones, countries, and service levels that may each have separate rate tables. Treat each combination as its own table when entering band and price values.
• Rounding and thresholds: Official calculations may use specific rounding rules (for example, to the next 10 g or 500 g). Adjust your band sizes and interpretation of the result accordingly.
• Letter size rules change over time: The letter dimension fields provide a basic size sanity check only. For exact small, large, or other letter categories, confirm the latest limits on the Australia Post site.
• Data updates: Australia Post can update prices, zones, and cubic divisors without notice. Revisit your rate table entries whenever you become aware of a change.

For final, binding postage costs, including any special services or promotions, rely on the official Australia Post calculators, counter quotes, or current price lists.

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.