The carrier logo on the label
Every printed parcel label carries the carrier's logo or product name near the top. If the label is in front of you, that is the fastest path. Numbers alone come into play when a merchant email includes only the digits.
Number format
Reading a tracking number to find the carrier
A tracking number's length and its first characters are enough to name the carrier that printed the label without opening a single site. The table below covers the four networks that account for almost every US parcel, and points at the exact tracker page each format belongs to.
Four networks, four number shapes
| Carrier | Length and shape | Tracker |
|---|---|---|
| USPS | Most commonly 22 digits, sometimes 26 or 30. Certified Mail starts 9407, Priority Mail Express starts EA - EM followed by nine digits and US, Registered Mail starts RA - RZ. International inbound uses two letters + nine digits + US. | tools.usps.com/go/TrackConfirmAction |
| UPS | 18 characters starting 1Z, then six-digit shipper number, two-digit service code and eight-digit package identifier. Mail Innovations uses a 22-digit numeric string that also tenders through USPS for final mile. | ups.com/track |
| FedEx | 12 or 15 digits for Express and Ground, 20 or 22 digits for SmartPost (final mile by USPS). Freight bill-of-lading numbers are 9 digits. | fedex.com/apps/fedextrack/ |
| DHL Express | 10 digits, occasionally with a hyphenated three-digit prefix. DHL eCommerce uses a longer alphanumeric string starting GM or LX. | dhl.com/tracking |
The prefixes matter. A USPS number that begins EA is Priority Mail Express, so a status stuck on Acceptance for two days is unusual and worth an inquiry. A UPS number without the 1Z prefix is almost always Mail Innovations, which is a UPS product handed off to USPS for the last leg - tracking it on ups.com will show the network switch and then go quiet until USPS scans it.
Two clues before the digits
The barcode symbology
USPS uses Intelligent Mail barcodes with a distinctive four-state bar pattern. UPS uses MaxiCode - a square of hexagons - alongside the linear code. FedEx uses a horizontal barcode and its Ship Manager font. DHL uses standard Code 128. A phone camera in a scanner app names the symbology in most cases.
The tracking email
The system that sent you the number almost always names the carrier in the subject line or the button label. A scan of your inbox for the sender's order confirmation resolves most cases without inspecting the digits.
When the number does not resolve
A regional last-mile carrier such as OnTrac, LaserShip (now Purolator) or LSO uses its own numbering and does not appear on the four major trackers. If a parcel began its journey on FedEx SmartPost or UPS SurePost, the middle of the trip may go dark and reappear on USPS once the handoff happens; the same is true in reverse. Our own tracking page recognises the major numbering families and routes to the correct tracker automatically.
Sources
- USPS Postal Service, Tracking & Confirmation - accepted number formats. Read 2026-08-11.
- USPS Postal Service, Where is my package? - number families and prefixes. Read 2026-08-11.
- UPS, Tracking - 1Z prefix and length. Read 2026-08-11.
- FedEx, Track shipments - digit counts for Express, Ground and SmartPost. Read 2026-08-11.
- DHL, Shipment tracking - Express and eCommerce number families. Read 2026-08-11.
Common questions
How can I tell which carrier a tracking number is from?
Look at the length and the first characters. 1Z starts every UPS number. USPS numbers are usually 22 digits or begin with two letters and end in US. FedEx uses 12 to 20 digits with no letters. DHL Express is 10 digits.
Does UPS mail innovations track on ups.com?
It shows up to the USPS handoff, then the last leg is scanned by USPS. Tracking on ups.com will pause and pick up only when USPS confirms delivery.
Why does my FedEx SmartPost tracking go quiet?
SmartPost hands to USPS for final delivery. FedEx tracking updates until then and USPS Tracking takes over at Out for Delivery.
What if the number does not work on any of the four trackers?
It is likely a regional carrier such as OnTrac, LSO or Purolator, or an internal order number the merchant labeled as tracking. Ask the sender which carrier they printed the label with.
Can I paste any format into SMKlog tracking?
Yes. The tracking page detects the format and forwards to the right carrier without asking you to pick.