Measure the packed parcel and enter the quoted price

How Australia Post chargeable weight is calculated

Australia Post explains that parcels can be assessed using physical weight or cubic weight. Cubic weight represents the vehicle space occupied by a parcel. For own packaging, the chargeable basis is generally the greater of the two under the applicable service rules.

Measure external length, width and height at their maximum points after the parcel is closed. Convert centimetres to metres, multiply the three dimensions to get cubic metres, then multiply by the published conversion factor of 250 kilograms per cubic metre.

The default example mirrors Australia Post’s published method: 50.5 cm x 40.3 cm x 30.9 cm is approximately 0.0628 m3. Multiplying by 250 gives about 15.72 kg, which is higher than a 10 kg physical weight.

Rate guides can round a chargeable weight into a price step. This worksheet reports the unrounded cubic result so you can enter it correctly into the official price calculator. It does not invent the zone, rounding or contract price.

Eligible flat-rate packaging follows a different path

Australia Post says eligible branded flat-rate packaging sent within Australia at 5 kg or under is priced by packaging size rather than cubic weight. The calculator uses physical weight as the displayed basis when that exact path is selected and the parcel is no more than 5 kg.

Not every Australia Post box or satchel is automatically eligible. The product must carry the relevant flat-rate size designation, and the contents must fit properly within the packaging. Packaging cost may be separate from postage.

If the physical weight exceeds 5 kg, the worksheet returns to the greater-of-physical-or-cubic comparison and flags the flat-rate assumption for review. It does not decide whether the article can travel in that packaging.

Prepaid products, MyPost Business, contract products, returns and international services can have different conditions. Use the correct current guide for the account and service actually being purchased.

Screen common domestic retail parcel dimensions

Australia Post’s published domestic parcel information identifies common Post Office limits of 22 kg maximum physical weight, 105 cm maximum length and 0.25 m3 maximum cubic volume. Particular services, contracts, destinations and facilities may apply other limits.

The result message compares the entered parcel with those three headline figures. Passing the screen does not guarantee acceptance. Shape, dangerous or prohibited goods, packaging, address, contents and service-specific conditions still matter.

Do not split or compress packaging in a way that damages the item. Sometimes a slightly smaller carton reduces cubic weight; sometimes protective packaging is worth the higher price. Product safety comes first.

Why the base postage remains an input

Postage depends on origin, destination, delivery speed, packaging, chargeable weight, features, customer account and current prices. Australia Post announced retail parcel price changes effective 1 July 2026, illustrating why a hard-coded table can become wrong.

Obtain the base price from the official online calculator, current Post Charges Guide, MyPost Business account or Post Office. Enter only the postage component before optional features. If the quote already includes signature, cover or packaging, leave those separate fields at zero to avoid double-counting.

The discount field applies only to base postage in this worksheet. Actual account discounts may apply to different components or be replaced by band pricing. Enter the final quoted base instead when the discount structure is unclear.

Fuel and other business surcharges can change by period and contract. Use the surcharge field for an amount already calculated under the applicable agreement; do not apply a public percentage to a retail quote without checking whether it belongs.

Measure and pack before requesting the price

Weigh the parcel after adding the carton, satchel, padding, tape, label and documents. Product-only weight understates the lodged article. Use scales suited to the range and record enough precision for the price step.

Measure the finished external package, not internal carton dimensions. Bulging sides, loose flaps, handles and irregular ends can increase the scan. For tubes and non-rectangular articles, follow Australia Post’s current measuring instructions.

Remove unnecessary empty space with suitable packaging, but retain cushioning and structural strength. A carton that collapses can damage contents, jam processing equipment or change dimensions.

Check the delivery address and postcode before buying postage. Zone selection for heavier parcels depends on origin and destination. An incorrect postcode can change both price and delivery estimate.

Separate delivery features from compensation assumptions

Tracking, signature, included compensation and optional cover are product terms, not interchangeable labels. Read what is included, the evidence required for a claim, excluded contents and maximum liability.

Enter a signature or cover price only after confirming eligibility. Extra cover does not make poor packaging acceptable and may exclude particular valuables or prohibited goods.

For a business, packaging, label printing, labour, failed delivery, returns and customer support can exceed the carrier charge. The per-parcel result is a transport worksheet, not a complete fulfilment cost.

Use the quantity result carefully

The quantity field multiplies identical per-parcel inputs. It does not create a bulk-mail, contract or MyPost Business quote. If dimensions, weights or destinations vary, calculate each parcel separately.

For ecommerce, store actual packed dimensions by product combination rather than one average. Large errors often occur when two products require a different carton from either product alone.

Reconcile purchased labels with carrier adjustments. Repeated underpaid-postage charges usually indicate incorrect master data, packing variation or measurement procedure. Update the source measurement rather than adding an unexplained buffer forever.

Worked example: separate measurement from the price quote

Consider a 10 kg parcel measuring 50.5 cm by 40.3 cm by 30.9 cm in own packaging. Its volume is about 0.0628 m3. At the 250 factor, cubic weight is about 15.72 kg, so the cubic figure is the relevant measurement basis rather than the lighter physical weight.

That 15.72 kg result is not itself a dollar price. The sender still supplies origin and destination postcodes, service speed, parcel details and account information to the current official pricing channel. A price table may round into a charging step or apply a route-specific amount.

Suppose the official base quote is $28.40, packaging costs $2.20 and no optional features are added. The worksheet total is $30.60 for one parcel. If a verified account discount of 10% applies only to the base, discounted base becomes $25.56 and total becomes $27.76. The packaging cost is not discounted by this model.

Keep the measurement result beside the official quote reference and date. If Australia Post changes retail prices or the business moves to another rate band, the physical parcel calculation remains useful while the price inputs are replaced.

Do not reuse the domestic screen for international mail

International services can have country, route, customs, aviation, dimension, weight, prohibited-goods and documentation rules that differ from domestic parcels. This page calculates geometric cubic weight, but its 22 kg, 105 cm and 0.25 m3 messages are explicitly a referenced domestic retail screen.

Use the official international quote and destination guide. Describe contents accurately, provide values and tariff information where required, and check whether taxes or duties are collected from the sender or receiver. A postage charge does not estimate destination import costs.

Delivery estimates are not guarantees and may exclude customs processing or disruption. Keep proof of lodgement and choose features suited to the contents and risk, based on the actual product terms.