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Postcodes in Australia are used to more efficiently sort and routemail in the Australian postal system.Postcodes in Australia have four digits and are placed at the end of the Australian address, before the country. Postcodes were introduced in Australia in 1967 by thePostmaster-General's Department and are now managed byAustralia Post, Australia's national postal service. Postcodes are published in booklets available frompost offices or online from the Australia Post website.

Australian envelopes and postcards often have four boxes printed in orange at the bottom right for the postcode. These are used to assist with the automated sorting of mail that has been addressed by hand for Australian delivery.

Postcodes were introduced in Australia in 1967 by thePostmaster-General's Department (PMG) to replace earlier postal sorting systems, such asMelbourne's letter and number codes (e.g.,N3,E5) and a similar system then used in rural and regionalNew South Wales. The introduction of the postcodes coincided with the introduction of a large-scale mechanical mail sorting system in Australia,^[1] starting with the Redfern Mail Exchange inSydney.^[2]

The initial digit of each postcode was copied directly from the previously-existing numerical prefixes ofAustralian radio call signs, which were based on state/territory borders. Over time, however, the initial digits of postcodes have deviated from the radio system, for example, the 8000 series refers to special addresses in Victoria. It is sometimes stated, incorrectly, that the initial digits of the postcodes corresponded to the geographical boundaries of the officialAustralian Military Districts,^[3] that existed in 1911–1997. In fact, only the boundaries of the initial 2- and initial 3– postcodes were ever similar to the former2nd and former3rd Military Districts, respectively.

By 1968, 75% of mail was using postcodes, and in the same year post office preferred-size envelopes were introduced,^[1] which came to be referred to as "standard envelopes".

Postcode squares were introduced in June 1990^[4] to enable Australia Post to useoptical character recognition (OCR) software in its mail sorting machines to automatically and more quickly sort mail by postcodes.

Australian postcodes consist of four digits,^[5] and are written after the name of the city, suburb, or town, and the state or territory:

Recipient Name
100 Citizen Road
BLACKTOWN NSW 2148

When writing an address by hand, and a row of four boxes is pre-printed on the lower right-hand corner of an envelope, the postcode may be written in the boxes instead. When posting to an organisation, business names can be written instead of a recipient name. If an article is intended for a specific identity within an organisation, their identity can be prepended on the line above the business name, withc/- prepended to the business name.

If addressing a letter from outside Australia, the postcode is recorded before 'Australia', which is placed on a fourth line.

Australian postcodes are sorting information. They are often linked with one area; e.g. 6160 belongs only toFremantle, Western Australia. Due to postcode rationalisation, they can be quite complex, especially in country areas; e.g. 2570 belongs to twenty-two towns and suburbs aroundCamden, New South Wales. The south-westernVictoria 3221 postcode of theGeelong Mail Centre also includes twenty places around Geelong with very few people. This means that mail for these places is not fully sorted until it gets to Geelong.^{[citation needed]} Some postcodes cover large populations (e.g., postcode 4350 serving some 100,000 people inToowoomba and the surrounding area), while other postcodes have much smaller populations, even in urban areas. Australian postcodes range from 0200 for theAustralian National University (now 2601) to 9944 forCannonvale, Queensland.

Some towns and suburbs have two postcodes — one for street deliveries and another forpost office boxes. For example, a street address in the Sydney suburb ofParramatta would be written like this:

Mr John Smith

99 George Street

PARRAMATTA NSW 2150

But mail sent to a PO Box in Parramatta would be addressed:

Mr John Smith

PO Box 99

PARRAMATTA NSW 2124

Many large businesses, government departments and other institutions receiving high volumes of mail had their own postcode as aLarge Volume Receiver (LVR), e.g. theRoyal Brisbane and Women's Hospital has the postcode 4029, theAustralian National University had the postcode 0200. More postcode ranges were made available for LVRs in the 1990s. Australia Post has been progressively discontinuing the LVR programme since 2006.^{[citation needed]}

Some places in Australia do not have postcodes. These are typically remote areas with little or no population.

The first one or two numerals usually show the state or territory that the postcode belongs to

Sometimes near the state and territory borders, Australia Post finds it easier to send mail through a nearby post office that is across the border:

Some of the postcodes above may cover two or more states. For example, postcode 2620 covers both a locality in NSW (Gundaroo) as well as a locality in the ACT (Hume), and postcode 0872 covers a number of localities across WA, SA and NT.

Three locations (Mingoola,^[6] Mungindi^[7] and Texas^[8]) straddle the NSW-Queensland border (so same town name and postcode on both sides).

Jervis Bay Territory is located on the coast of NSW. It is just south of the towns of Vincentia and Huskisson, with which it shares a postcode. Mail to the Jervis Bay Territory is addressed to the ACT.

The numerals used to show the state on each radio callsign in Australia are the same numeral as the first numeral for postcodes in that state, e.g.2xx in New South Wales,3xx in Victoria, etc. Radio callsigns pre-date postcodes in Australia by more than forty years.

Australia's external territories are also included in Australia Post's postcode system. While these territories do not belong to any state, they are addressed as such for mail sorting:

Three scientific bases in Antarctica operated by theAustralian National Antarctic Research Expeditions share a postcode with the isolated sub-Antarctic island ofMacquarie Island (part of Tasmania):

There is also a "special" postcode for routing mail sent toSanta Claus:

Each state's capital city ends with three zeroes, while territorial capital cities end with two zeroes. Capital city postcodes were the lowest postcodes in their state or territory range, before new ranges for LVRs and PO Boxes were made available. The last numeral can usually be changed from "0" to "1" to get the postcode forGeneral Post Office boxes in any capital city (though Perth now uses a different range of postcodes for its GPO Boxes):

While the first numeral of a postcode usually shows the state or territory, the second numeral usually shows a region within the state. However, postcodes with the same second numeral are not always next to each other. As an example, postcodes in the range 2200–2299 are split between the southern suburbs of Sydney and theCentral Coast,Lake Macquarie andNewcastle regions of New South Wales.

Postcodes with a second numeral of "0" or "1" are almost always located within the metropolitan area of the state's capital city. Postcodes with higher second numerals are usually located in rural and regional areas. Common exceptions are where towns were rural when postcodes were first introduced in 1967, but have since been suburbanised and incorporated into metropolitan areas, e.g.Penrith, New South Wales has the postcode 2750 andPetrie, Queensland has the postcode 4502.

Within each region with the same second numeral, postcodes are usually allocated in ascending order the further one travels from the state's capital city along major highways and railways. For instance, heading north on theNorth Coast railway in New South Wales away from Sydney:

Major towns and cities tend to have "0" as the last numeral or last two numerals, e.g.Rockhampton, Queensland has the postcode 4700 andBallarat, Victoria has the postcode 3350. There are exceptions; the major town ofIpswich, Queensland has the postcode 4305, whileGoodna, a relatively small suburb of Ipswich, is allocated 4300.

Australia Post prefers envelopes sold in Australia to have four boxes in the bottom right corner of the front of the envelope. Entering the postcode in these boxes or squares, which Australia Post callspostcode squares, enables Australia Post to useoptical character recognition software in its mail sorting machines to automatically and more quickly sort mail into postcodes, which also embeds routing information. Postcode squares were introduced in June 1990.^[4]

Australia Post says that postcode squares should not be used for machine-addressed mail, or mail going overseas.

Many other organisations now use postcodes.Insurance companies often use postcodes when working out the cost of car and house insurance.Transport for NSW uses postcodes to give specific numbers for each bus stop inGreater Sydney. The stop number is five to seven numbers: the first four are the postcode, and the others show the bus stop (sometimes written with a space in between, e.g. "2000 108").

Many companies that produce metropolitan street maps also list the postcodes for each suburb, both in indexes and on the maps themselves. Spatial representation of postcodes is also very popular in defining sales and franchise territories.

Australian Bureau of Statistics, Australian Taxation Office and many other Federal and State government organisations publish a variety of statistics by postcode which extends the use Australia Post four digit code to many business and social planning related activities.

There is an inherent problem with spatial representation of postcodes since areas referenced to a specific postal code tend to change over time, as new postcodes are added or existing ones are split by Australia Post for operational purposes.^[10]

Some mail generating software can automatically sort outward mail by postcode before it is generated. This pre-sort of mail into postcode order eliminates the need for it to be sorted manually or usingmail sorting machines.

To improve mechanised sorting, each address now has a sorting number which is printed on the letter as an orange-colouredbarcode.^[11] This number might be 12 digits long. This system enables the post office to place items in delivery order. Companies can also use Rapid Addressing Tool (RATS) to print Customer Addressed Barcodes, which are printed above the address. Every Delivery Point in Australia (DPID) has its own number. Barcode sorter machines sort and sequence letters up to C5 size. Flat multi-levelOCR reads, imprints and sorts C5 to A3 sized articles.

• Postal codes in Canada
• Postcodes in the United Kingdom
• Postcodes in New Zealand
• ZIP code in USA

• Postcodes Australia - Australia Post's postcode search
• Australian Bureau of Statistics data related to postcodes
• Free Australia postcode maps by state and city
• Public domain database (XLS,CSV,XML,JSON) of Australia postcodes and geographical data

• Postcodes in Australia
• Postal codes by country
• Postal history of Australia

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