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ZIP+4 lookup, and why a parcel rarely needs one

The four digits after the hyphen name a slice of a five-digit ZIP: the first two are a sector, the last two a segment such as one side of a city block or a single floor of a building. On a parcel label you can leave them off, because the five-digit ZIP is what sets the price and the network codes the rest itself. Treat this page as reference material; SMKlog sells US domestic parcel labels bought as a guest, and we do not sell mailing-list software, fulfillment or platform integrations.

USPS definitions quotedEight live quotesCaptured 2026-07-28
Price a box by its five-digit ZIPs
ZIP code digits mapped to a delivery segment
Two digits, then two more

Sector and segment are defined verbatim in the Postal Service address products guide, fetched 2026-07-28.

Eight ZIPs, one box, and no +4 anywhere: quoted 2026-07-28

To show which part of a ZIP does the pricing, we sent the same 12 x 10 x 6 in box at 5 lb to eight destinations from one origin on one day. Only the five-digit destination changed. No ZIP+4 was supplied on any of the eight.

Quoted from Newark, NJ 07102 on 2026-07-28 through the SMKlog calculator. Cheapest returned rate per destination; the gap column subtracts the Hoboken figure.
DestinationCityCheapest quoteGap from the local lane
07030Hoboken, NJ$10.37baseline
19102Philadelphia, PA$10.37no change
30303Atlanta, GA$13.52plus $3.15
60601Chicago, IL$14.02plus $3.65
75201Dallas, TX$15.49plus $5.12
80202Denver, CO$16.47plus $6.10
90011Los Angeles, CA$19.14plus $8.77
98101Seattle, WA$19.14plus $8.77

Eight destinations, an $8.77 spread, and the last four digits never entered the arithmetic. Notice the two ties as well: Hoboken and Philadelphia landed identically, as did Los Angeles and Seattle, because rates step between bands rather than sliding with distance.

Try your own pair of ZIPs

Sector first, then segment

The Postal Service address products guide defines the two halves precisely. A ZIP sector number "forms the first two digits of the ZIP +4 code. A ZIP sector is a subdivision of a 5-digit ZIP Code area." The segment is finer: "The ZIP segment is a subdivision of a ZIP sector, i.e., it represents areas such as one side of a city block between intersections; both sides of a street, including cul-de-sacs; a company or building; a floor or group of floors within a building; a cluster of mailboxes; sections of Post Office boxes; or other similar delivery groups." Both quotes come from the Address Information System Products Technical Guide on postalpro.usps.com, checked 2026-07-28.

Where the extra four really earn their keep

Bulk mail, not your box. The Postal Service explains that a routing code can carry a 5-digit ZIP, a 9-digit ZIP+4 or an 11-digit delivery point code, and that "To obtain automation discounts, a Delivery-Point ZIP Code from CASS-certified (Coding Accuracy Support System) software is required", per its own barcode instruction sheet on about.usps.com, checked 2026-07-28. A single parcel bought online is not claiming an automation price, so nothing rides on the add-on.

Writing it, if you write it at all

Publication 28 keeps punctuation out of the address block with one exception, stating that "With the exception of the hyphen in the ZIP+4 Code, punctuation may be omitted in the delivery address block." The last line wants at least one space between the city, the two-character state and the code, with two spaces preferred before it, per sections 222 and 224 at pe.usps.com, checked 2026-07-28. One oddity worth knowing: add-ons for places with no delivery, such as vacant lots, carry the letters ND in the segment position rather than digits.

ZIP+4 questions

What do the last four digits of a ZIP+4 mean?

The first two are a sector, a subdivision of the five-digit ZIP area. The last two are a segment, which the Postal Service describes as things like one side of a city block between intersections, a company or building, a floor or group of floors, a cluster of mailboxes, or a section of Post Office boxes, per the Address Information System Products Technical Guide on postalpro.usps.com, checked 2026-07-28.

Do I need a ZIP+4 to ship a package?

No. A five-digit destination ZIP is enough to price and buy a domestic parcel label, and the carrier assigns the finer code itself during sorting. Our own eight-destination test on 2026-07-28 priced every lane from the five-digit ZIP alone.

Where can I look up a ZIP+4?

The Postal Service runs an address lookup on usps.com that returns the full nine-digit code for a given street address. Any address tool graded under the CASS program pulls the same value out of the ZIP+4 file, which is why two tools agree when the address is complete.

Does a ZIP+4 change what shipping costs?

Not on a parcel. Price follows the origin and destination five-digit ZIPs, the box and the weight. In our 2026-07-28 quotes the same box ran $10.37 to Hoboken and $19.14 to Seattle with no add-on supplied on either.

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