POSTNET Barcode Generator — USPS Postal Routing Symbology: Generate USPS POSTNET barcodes online. Create 5-digit ZIP, 9-digit ZIP+4, and 11-digit delivery point barcodes with automatic Mod 10 checksum, vector SVG.
What is the USPS POSTNET Barcode Symbology?
POSTNET (an acronym for Postal Numeric Encoding Technique) is a specialized height-modulated one-dimensional barcode symbology introduced by the United States Postal Service (USPS) to automate the high-speed sorting and routing of letter mail. Unlike traditional retail barcodes (such as UPC-A or Code 128) where data is encoded by varying the horizontal widths of bars and spaces, POSTNET encodes data exclusively by altering the vertical heights of uniformly spaced black bars: every bar is either a Full Bar or a Half Bar.
Historically printed along the bottom lower-right edge of envelopes, POSTNET allowed automated optical character readers (OCR) and high-speed bar-code sorters (BCS) in USPS distribution centers to route letters directly to delivery carrier routes without manual sorting. While USPS has transitioned operational mail streams to the 4-state Intelligent Mail Barcode (IMb), POSTNET remains widely supported across legacy mailing software, corporate statement printing, and archival mail piece verification systems.
POSTNET Mathematical Encoding Principles & Structure
A POSTNET barcode consists of five distinct structural components:
- Leading Framing Bar: Exactly one full-height bar marking the start of the code.
- Payload Data Bars: Encodes the ZIP code digits using a discrete 2-out-of-5 binary code.
- Correction Check Digit: Exactly 5 bars representing a Modulo-10 checksum.
- Trailing Framing Bar: Exactly one full-height bar marking the termination of the barcode.
The 2-out-of-5 Weighted Binary Code Table
Every decimal digit from $0$ to $9$ is encoded using exactly five consecutive bars. Exactly two of those five bars are Full Bars ($1$), and exactly three are Half Bars ($0$). The first four bars correspond to the arithmetic place values $7, 4, 2, 1$. The final fifth bar acts as an internal single-digit parity check. When the sum of the weighted bits is $11$ (the exceptional case for digit $0$), the code uses $7+4=11$:
| Digit | Binary Representation (1=Full, 0=Half) | Weights ($7 + 4 + 2 + 1 + 0$) | Visual Height Geometry |
|---|---|---|---|
| 1 | 0 0 0 1 1 | $0 + 0 + 0 + 1 + 0 = 1$ | Half, Half, Half, Full, Full |
| 2 | 0 0 1 0 1 | $0 + 0 + 2 + 0 + 0 = 2$ | Half, Half, Full, Half, Full |
| 3 | 0 0 1 1 0 | $0 + 0 + 2 + 1 + 0 = 3$ | Half, Half, Full, Full, Half |
| 4 | 0 1 0 0 1 | $0 + 4 + 0 + 0 + 0 = 4$ | Half, Full, Half, Half, Full |
| 5 | 0 1 0 1 0 | $0 + 4 + 0 + 1 + 0 = 5$ | Half, Full, Half, Full, Half |
| 6 | 0 1 1 0 0 | $0 + 4 + 2 + 0 + 0 = 6$ | Half, Full, Full, Half, Half |
| 7 | 1 0 0 0 1 | $7 + 0 + 0 + 0 + 0 = 7$ | Full, Half, Half, Half, Full |
| 8 | 1 0 0 1 0 | $7 + 0 + 0 + 1 + 0 = 8$ | Full, Half, Half, Full, Half |
| 9 | 1 0 1 0 0 | $7 + 0 + 2 + 0 + 0 = 9$ | Full, Half, Full, Half, Half |
| 0 | 1 1 0 0 0 | $7 + 4 + 0 + 0 + 0 = 11 implies 0$ | Full, Full, Half, Half, Half |
Check Digit Calculation Algorithm
The POSTNET check digit ensures total packet integrity. The check digit $C$ is chosen such that when it is added to the sum of all preceding payload digits, the grand total is an exact multiple of 10:
$$S = sum_{i=1}^{n} D_i$$ $$C = (10 - (S pmod{10})) pmod{10}$$Worked Example (ZIP+4): Consider the code $90210 ext{-}1234$:
- Sum of digits: $9 + 0 + 2 + 1 + 0 + 1 + 2 + 3 + 4 = 22$.
- $22 pmod{10} = 2$.
- Check digit: $(10 - 2) pmod{10} = mathbf{8}$.
- Verification: $22 + 8 = 30$, which is cleanly divisible by 10.
- The total barcode encodes 10 digits ($9$ payload digits $+ 1$ check digit $= 50$ bars), plus $2$ framing bars $= mathbf{52 ext{ bars}}$ total.
Three Standard POSTNET Formats
- 5-Digit Standard ZIP Code: Contains 5 payload digits + 1 check digit + 2 frame bars $= 32 ext{ bars}$. Used for preliminary regional destination sort.
- 9-Digit ZIP+4 Code: Contains 9 payload digits + 1 check digit + 2 frame bars $= 52 ext{ bars}$. Pinpoints geographic delivery sectors or street blocks.
- 11-Digit Delivery Point Barcode (DPBC): Contains 9-digit ZIP+4 + 2 delivery point digits (typically the last 2 digits of the street address number) + 1 check digit + 2 frame bars $= 62 ext{ bars}$. Enables automated carrier-route sequencing down to the individual mail slot.
Real-World Industry Applications
- Transactional Statement Mailings: Utility companies, financial institutions, and medical providers print POSTNET codes on bulk monthly invoices and statements for discounted postal automation rates.
- Direct Mail Advertising Campaigns: Marketing agencies generate postal barcodes on postcards and catalogs to qualify for USPS automation discounts.
- Return Envelopes (BRE): Business Reply Envelopes feature pre-printed POSTNET barcodes to guarantee rapid return routing to corporate billing departments.
- Legal & Court Notice Verification: Process servers and municipal agencies record postal barcodes as verifiable proof of proper address formatting on official notices.