What is a Card Format? Understanding the Technical Structure of a Proximity Card
In the world of access control and security systems, the term “card format” comes up often—especially when working with proximity (prox) cards. Card formats are a behind-the-scenes but critical part of ensuring your system runs smoothly, securely, and without hiccups.
If you’ve ever wondered what a card format actually is and why it matters, this guide will walk you through the essentials—how it works, why it’s important, and what to consider when choosing one.
Defining a Card Format
A card format is essentially the blueprint for how data is stored on an access card. It determines the specific structure in which information—such as a cardholder’s unique ID number, facility code, or other credentials—is arranged.
Think of it like a filing system: the data on the card must be stored in an exact order so your access control system can read, interpret, and verify it correctly. Without the right format, the system won’t know how to process the information, and the card won’t function for granting access.
Key Components of a Card Format
Most card formats include a few standard elements:
Card Number (ID): A unique identifier tied to each user.
Facility Code: A code that tells the system which building, site, or organization the card is associated with.
Bit Length: The total number of bits in the format—common options include 26-bit, 34-bit, or custom configurations.
Start & Stop Bits: Markers that indicate where the data begins and ends in the format.
Common Card Formats
26-Bit Wiegand: The industry’s most widely used format, offering a simple structure that includes both a card number and facility code.
Custom Formats: Organizations with higher security demands often opt for custom layouts, such as 34-bit or 37-bit formats, which allow for more unique IDs and greater protection against duplication.
Card Formats for Prox Cards
Proximity cards (prox cards) are a popular choice for businesses, campuses, and government buildings. These cards communicate with readers using RFID (radio-frequency identification) technology—no swiping required.
The card format determines how the prox card’s data is structured and interpreted. For example, a typical 26-bit format might include:
8 bits for the facility code (up to 256 possibilities)
16 bits for the card number (up to 65,536 unique IDs)
2 bits for start/stop markers
When a card is presented to a reader, the system decodes this information and checks whether it matches an authorized user in the database.
Why Card Formats Matter
The right card format is essential for:
Compatibility: Not all systems read every format. If your readers are set for 26-bit, they won’t understand a 37-bit card.
Security: Larger or custom formats increase the number of possible ID combinations, making cloning harder.
Scalability: Your format determines how many unique cards you can issue—important if your organization is growing.
Customization: Custom formats can include additional data fields or more complex numbering for enhanced security.
Choosing the Right Format
When selecting a card format, consider:
Security Requirements – Higher bit lengths and custom formats reduce duplication risks.
System Compatibility – Verify your format works with all readers and control systems.
Future Expansion – Ensure you’ll have enough unique card numbers as your user base grows.
Final Thoughts
A card format is more than a technical detail—it’s the foundation of how your access control system identifies and authenticates users. Whether you choose a standard 26-bit or a custom high-security format, understanding your options will help you build a system that’s secure, compatible, and ready for the future.
If you need help selecting the right card format for your facility, contact us today our team can guide you through the process and ensure your cards work seamlessly with your security setup.