Royal Mail

What is a Royal Mail barcode?

Royal Mail 4-State Customer Code (RM4SCC, also called CBC — Customer Bar Code) is the barcode symbology used by Royal Mail (UK postal service) for automated sorting of addressed mail. Like POSTNET, it encodes data in bar height rather than bar width — but uses four bar heights (full ascender, full descender, both ascender+descender, and short tracker bar) instead of two. RM4SCC encodes the UK postcode plus a delivery point suffix, enabling Royal Mail's sorting machines to route mail to the correct walk sequence for delivery.

Four-state bar encoding

RM4SCC uses four distinct bar heights:

• Full ascender (A): Bar rises above the track line.
• Full descender (D): Bar drops below the track line.
• Full bar (F): Both ascender and descender.
• Tracker (T): Short bar at track height only.

Each character is represented by a sequence of these four states. The symbology encodes alphanumeric data (0–9, A–Z) plus a start character, stop character, and a Reed-Solomon check character. The postcode, delivery point code, and a check character are encoded in sequence.

Check character (Reed-Solomon mod 6)

RM4SCC appends a single check character calculated using a Reed-Solomon Modulo 6 algorithm over all data codeword values. The check character is appended before the stop bar. Unlike simple Modulo 10 checks, Reed-Solomon provides burst error detection across multiple characters, improving reliability in high-speed postal sorting environments.

RM4SCC vs. POSTNET vs. IMB

RM4SCC (4 bar heights), POSTNET (2 bar heights), and USPS Intelligent Mail Barcode (4 bar heights) all encode postal routing data in bar height rather than width — but each is specific to its national postal service and incompatible with the others. RM4SCC is exclusive to Royal Mail UK; POSTNET/IMB are exclusive to USPS.

When to use Royal Mail RM4SCC

RM4SCC is used on:

• Addressed mail and business mailings qualifying for Royal Mail automation discounts (Mailmark and older CBC formats).
• Direct mail campaigns printed by mailing houses integrated with Royal Mail's Postcode Address File (PAF).

RM4SCC must be generated using Royal Mail-approved software that validates postcodes against the PAF database. Self-generation without PAF validation is not permitted. Note: Royal Mail has largely transitioned to the newer Mailmark barcode (2D DataMatrix) for new implementations.

Printing requirements

Bar height specifications: full ascender 5.1 mm, tracker 2.1 mm, full descender 5.1 mm below tracker, full bar 10.2 mm total. Bar width: 0.6 mm uniform. Bar pitch: 1.25 mm centre-to-centre. Print in black on white or cream paper; avoid coloured envelopes. Placement: within the address barcode area defined by Royal Mail (typically bottom of the envelope).

Common scanning failures

Bar height discrimination is critical for RM4SCC — inkjet printers with insufficient vertical resolution can fail to clearly differentiate the four bar heights. Environmental moisture that causes paper to expand vertically can also alter bar height ratios. Royal Mail requires mailers to use approved production software and submit samples for quality approval before high-volume mailings.