# NPA/NXX

NPA/NXX is the North American Numbering Plan's name for the first six digits of a US or Canadian number: the area code and the central office code.

Date: 2026-09-10

NPA/NXX is the North American Numbering Plan's name for the first six digits of a US or Canadian number: the three-digit area code (Numbering Plan Area) and the three-digit central office code (NXX). Numbers are allocated to carriers in blocks keyed on those six digits, and the regulators publish the tables.

## What Spaw answers

The block behind a number sets three fields. `block_status` says what the table records — allocated, unassigned or reserved. `carrier` names the block holder as the regulator lists it. `line_type_source` says `block_allocation` when the block, rather than the numbering plan, settled the line type.

That last one is the whole reason the tables are carried. The plan itself cannot separate American mobiles from landlines, because they share blocks; it can only answer `fixed_line_or_mobile`. The block holder often settles it — a wireless carrier's block is mobile, a virtual-number wholesaler's is VoIP.

## What it does not know

A block describes the original allocation, never a later port. A number moved to another carrier keeps the block it was born in, so `carrier` is who the numbers were given to and not who serves the handset today.

Every area code with published blocks has a page of its own under [the phone lookup](/tools/phone-number-lookup).

Reference: https://spaw.co/glossary/npa-nxx