Wiegand bit formats define how credential data is structured and transmitted within an access control system. While the Wiegand interface determines how data is electrically sent from a reader to a controller, the bit format determines how that data is organized and interpreted. The most commonly deployed formats today are 26-bit and 37-bit Wiegand structures.
When integrating readers, controllers, and credentials from different manufacturers, understanding Wiegand bit formats is essential to ensure compatibility and reliable system performance.
This guide explains how Wiegand data is organized, how 26-bit and 37-bit formats are structured, and why correct format configuration directly affects integration success.
What is a Wiegand Bit Format?
A Wiegand bit format defines the structure of the binary data transmitted from a credential reader to an access control panel.
When a card or credential is presented, the reader sends a sequence of bits over the Wiegand interface. The controller interprets those bits according to a predefined layout.
A bit format determines:
- The total number of bits transmitted
- Which bits represent the facility or site code
- Which bits represent the credential or card number
- Which bits are reserved for parity
If the reader and controller are not configured for the same bit format, the credential data may be misinterpreted or rejected.
General Structure of a Wiegand Format
Most Wiegand formats follow a similar structural pattern:
- A leading parity bit
- A facility or site code field
- A credential or card number field
- A trailing parity bit
Parity bits provide basic error detection. They allow the controller to verify that the transmitted bit stream was received correctly. However, parity does not encrypt data or provide protection against interception.
The number of bits assigned to each section varies depending on the format.
The 26-Bit Wiegand Format
The 26-bit Wiegand format is one of the most widely used legacy structures, particularly in North America.
A standard 26-bit layout typically includes:
- Bit 1: Even parity
- Bits 2–9: 8-bit facility code
- Bits 10–25: 16-bit card number
- Bit 26: Odd parity
Capacity and Limits
- Facility codes range from 0 to 255
- Card numbers range from 0 to 65,535
- Each facility code supports up to 65,536 unique card numbers
Because of its limited size, 26-bit Wiegand can create duplication risks in larger or multi-site deployments. Despite this limitation, it remains common in existing infrastructure and smaller systems.
The 37-Bit Wiegand Format
As credential populations expanded and enterprise deployments grew, longer bit formats were introduced to provide greater scalability. The 37-bit Wiegand format is widely used as a higher-capacity alternative to 26-bit.
Unlike 26-bit, 37-bit formats are not universally identical across manufacturers. However, one commonly deployed structure follows a consistent and widely recognized layout.
Common 37-Bit Format Breakdown
A widely used 37-bit configuration is structured as follows:
- Bit 1: Even parity
- Bits 2–17: 16-bit facility code
- Bits 18–36: 19-bit card number
- Bit 37: Odd parity
What This Allocation Means
16-bit Facility Code (Bits 2–17)
Supports up to 65,536 facility or site codes, significantly expanding beyond the 8-bit limitation of 26-bit formats.
19-bit Card Number (Bits 18–36)
Supports up to 524,288 unique card numbers per facility code.
Parity Bits (Bits 1 and 37)
The leading parity bit typically validates the first portion of the data field, while the trailing parity bit validates the remaining portion.
This expanded allocation significantly reduces the likelihood of duplicate credentials across large multi-site or enterprise deployments.
Because 37-bit implementations may vary slightly by manufacturer, it is important to confirm the exact bit layout and parity rules during system configuration.
Custom and Extended Wiegand Formats
Beyond 26-bit and 37-bit formats, many systems use extended or proprietary Wiegand structures such as:
- 35-bit
- 40-bit
- 48-bit
- Manufacturer-specific extended formats
These variations may adjust:
- Facility code length
- Card number length
- Parity placement
- Additional data segmentation
Custom formats are often implemented to:
- Increase credential capacity
- Support proprietary credential programs
- Align with enterprise security policies
- Maintain compatibility with legacy deployments
Both the reader and controller must be configured identically to ensure accurate credential interpretation.
Understanding Parity in 26-Bit and 37-Bit Formats
Parity bits serve as a basic validation mechanism.
In most implementations:
- The leading parity bit checks a defined portion of the data field for even parity
- The trailing parity bit checks another portion for odd parity
If parity validation fails, the controller may reject the credential read.
It is important to understand that parity provides transmission validation only. It does not encrypt the credential data or protect it from interception.
Why Bit Format Matching is Critical
One of the most common integration issues in access control deployments involves mismatched Wiegand formats.
For example:
- A reader outputs 37-bit data
- The controller expects 26-bit data
In this case, the controller will misinterpret the incoming bit stream. This can result in:
- Invalid reads
- Incorrect facility code assignments
- Access denial
- Duplicate credential conflicts
Before deployment, integrators should confirm:
- Total bit length
- Exact field allocation
- Parity configuration
- Controller compatibility
Proper documentation and configuration prevent installation delays and troubleshooting challenges.
Wiegand Formats in RFID and Vehicle Access Systems
In vehicle access environments that rely on RFID credentials or license plate recognition, Wiegand output remains common when integrating with existing access control panels.
Many gate controllers and legacy access platforms are designed to receive credential data through a Wiegand interface. As a result, both RFID readers and LPR cameras must transmit structured bit-format data that aligns with controller expectations.
TagMaster North America’s RFID readers and LPR cameras support configurable Wiegand output, including 26-bit and 37-bit formats. This enables seamless integration with legacy access control infrastructure while supporting expanded credential programs where required.
Security Considerations
While Wiegand bit formats define credential structure, they do not provide encryption.
Wiegand transmits credential data as raw binary over physical wiring. This means:
- Data can potentially be intercepted
- There is no device authentication
- There is no reader supervision
While Wiegand bit formats remain widely used, many modern systems are transitioning to encrypted communication protocols such as OSDP for enhanced security and device supervision.
Key Takeaways
- A Wiegand bit format defines how credential data is structured during transmission.
- The 26-bit format remains common in legacy access control systems.
- The 37-bit format significantly increases facility and credential capacity.
- Parity bits provide transmission validation but not encryption.
- Matching reader and controller configuration is essential for reliable operation.
Understanding 26-bit and 37-bit Wiegand formats helps system designers and integrators deploy scalable, compatible access and vehicle control systems with fewer integration challenges.