BSB Number Format Explained: What Each Digit Means

The Structure of a BSB Number

Every BSB (Bank-State-Branch) number in Australia follows the same six-digit format: XXX-YYY. While it may look like an arbitrary string of numbers, each digit carries specific meaning. The code is carefully structured to identify three things: the financial institution, the state or territory, and the individual branch.

Understanding this structure is useful for anyone who works with BSB numbers regularly, whether you are verifying payment details, reconciling transactions, or simply curious about how Australia's domestic payment routing works.

The Format: XXX-YYY

A BSB number is always six digits, conventionally written with a hyphen after the third digit. The two halves of the number serve different purposes:

• First three digits (XXX): Identify the financial institution and, in many cases, the state or territory
• Last three digits (YYY): Identify the specific branch

Some documentation breaks the first three digits down further into a two-digit institution code and a one-digit state code. However, this separation is not universal -- the exact allocation of meaning within the first three digits varies by institution, and some banks use the full three-digit prefix as a combined institution-and-state identifier.

Institution Codes: The First Two Digits

The leading digits of a BSB number identify the financial institution. The industry body that manages the BSB system assigns specific numeric ranges to each participating bank, credit union, or building society.

Major Bank Ranges

The four major Australian banks have well-known prefix ranges:

The "x" in each range represents the state digit, which is discussed in the next section.

Other Notable Institution Codes

Beyond the Big Four, many other financial institutions have assigned BSB prefix ranges:

Note that this is not an exhaustive list. The complete directory is maintained by the official industry body, and new codes are assigned as institutions join the system. Some ranges have been reallocated over time due to mergers and closures.

Why Some Banks Have Multiple Ranges

You may notice that some institutions appear under more than one prefix range. This typically occurs for one of two reasons:

1. Mergers and acquisitions: When one bank acquires another, the acquired bank's BSB range is retained alongside the parent bank's range. For example, Westpac's BSB range includes 03x (its original range) as well as 11x (St George), 10x (BankSA), and 19x (Bank of Melbourne), all of which are now divisions of Westpac.

2. Product or division separation: Some banks use different BSB ranges for different product lines or divisions. This allows internal routing to the correct processing system even within the same institution.

The State Code: The Third Digit

For many major banks, the third digit of the BSB number indicates the state or territory where the branch is located. The conventional state coding is:

How This Works in Practice

Using Commonwealth Bank (prefix 06) as an example:

• 062-xxx = CBA branch in New South Wales
• 063-xxx = CBA branch in Victoria
• 064-xxx = CBA branch in Queensland
• 065-xxx = CBA branch in South Australia
• 066-xxx = CBA branch in Western Australia
• 067-xxx = CBA branch in Tasmania

Similarly, for ANZ (prefix 01):

• 012-xxx = ANZ branch in New South Wales
• 013-xxx = ANZ branch in Victoria
• 014-xxx = ANZ branch in Queensland

Limitations of the State Code

The state code convention is most consistently applied by the Big Four banks and some other major institutions. However, it is not a universal rule:

• Smaller banks and credit unions may not follow this pattern, particularly if they operate primarily within a single state or territory.
• Online-only banks typically have a single BSB number for all customers regardless of location, so the state digit may not reflect any geographic distribution.
• Some institutions use the third digit for internal routing purposes unrelated to geography.

Always verify BSB details through an official source rather than assuming the state based on the third digit alone.

The Branch Code: The Last Three Digits

The final three digits of a BSB number -- the portion after the hyphen -- identify the specific branch within the institution and state. These are assigned by the financial institution itself, according to its own internal conventions.

Common Patterns

While there is no mandated standard for branch code assignment, some patterns are common:

• 000 or 001: Often assigned to the head office or primary processing centre in a given state. For example, CBA's BSB 062-000 corresponds to its primary NSW branch.
• Sequential numbering: Many banks assign branch codes sequentially as new branches open. Lower numbers tend to correspond to older, more established branches.
• Geographic clustering: Some institutions group branch codes by region within a state. For example, branches in the Sydney CBD might have codes in the 000-099 range, while branches in regional NSW might start at 500 or higher.

Examples

Here is how the full BSB breaks down for several real branches:

062-000 -- Commonwealth Bank, Sydney NSW - 06 = Commonwealth Bank - 2 = New South Wales - 000 = Head office / primary branch

033-088 -- Westpac, Collins Street Melbourne VIC - 03 = Westpac - 3 = Victoria - 088 = Collins Street branch

084-462 -- NAB, Perth WA - 08 = National Australia Bank - 4 = Queensland (note: NAB's state codes may differ from the standard convention in some cases) - 462 = Specific branch

012-003 -- ANZ, Sydney NSW - 01 = ANZ - 2 = New South Wales - 003 = Specific branch in NSW

Validating a BSB Number

Knowing the BSB format can help you perform a basic sanity check on any BSB number before using it:

Quick Validation Checklist

1. Length: A BSB number must be exactly six digits. No more, no fewer.
2. Characters: BSB numbers contain only numeric digits (0-9). If you see any letters, it is not a valid BSB.
3. Institution prefix: The first two digits should fall within a known institution range. If the prefix does not match any bank, the BSB may be invalid or incorrectly entered.
4. Active status: Even if a BSB is correctly formatted and matches a known institution, it may have been decommissioned due to a branch closure or merger. Always verify against a current directory.

Using BSBFinder to Validate

The most reliable way to validate a BSB number is to look it up. BSBFinder provides a free lookup tool that checks any six-digit code against the current BSB directory. Enter the number and the tool will confirm whether it is active and display the associated institution, branch name, and address.

Special Cases and Exceptions

BSB Numbers for Virtual Branches

With the decline of physical bank branches and the rise of online banking, many BSB numbers now correspond to virtual or centralised processing centres rather than brick-and-mortar locations. The format remains the same -- six digits in XXX-YYY format -- but the "branch" may be a data centre or administrative office rather than a shopfront where customers can walk in.

Credit Union BSB Numbers

Credit unions and building societies in Australia often use BSB ranges managed through Cuscal (prefix 80x) or other clearing house arrangements. The internal structure of these BSB numbers may differ from the Big Four convention, and the state digit may not follow the standard mapping.

Shared BSB Numbers

In rare cases, multiple products or account types within the same institution may share a single BSB number. This is common with online-only banks, where one BSB routes all transactions to a single processing system regardless of account type.

Summary

The BSB number format is a compact but information-rich code. The first two or three digits identify the financial institution (and often the state), while the last three identify the specific branch. While the general structure is consistent across the system, the specific conventions for state coding and branch numbering vary by institution. For reliable identification, always look up a BSB number using BSBFinder or the official BSB directory rather than relying solely on manual interpretation.