# Number pooling (thousands-blocks)

Number pooling splits a North American central office code into ten blocks of a thousand numbers, each assigned to a carrier separately, so one code can hold several carriers' numbers.

Date: 2026-09-27

Number pooling is the North American practice of splitting a central office code's 10,000 numbers into ten blocks of 1,000, the thousands-blocks written NPA-NXX-X, and assigning each block to a carrier separately. The US rule defines it as the process by which "the 10,000 numbers in a central office code (NXX) are separated into ten sequential blocks of 1,000 numbers each (thousands-blocks), and allocated separately within a rate center" (47 CFR 52.20(a), https://www.law.cornell.edu/cfr/text/47/52.20, accessed 27 September 2026). A pooled code can hold the numbers of several carriers, so the holder of the code is not necessarily the holder of a given number's block.

## How much of the plan is pooled

In NANPA's tables of 26 September 2026, 141,810 of the 197,177 central office codes assigned in the United States (71.9%) are pooled. The thousands-block report lists 1,303,876 blocks held inside those codes and 88,562 more that are free in the pool with none of their numbers still in use, and 663,918 of the held blocks (50.9%) are held under a different [operating company number](/glossary/operating-company-number) than the code they sit in. NANPA marks each block assigned (AS), retained (RT), available (AV), available pending (AP) or available with a future effective date (AF) (https://www.nanpa.com/reports/thousands-block-reports/region, accessed 27 September 2026). The Canadian administrator's table of 23 September 2026 marks 2 of its 28,710 assigned codes pooled. The [phone statistics page](/statistics/phone) carries the US counts and is measured again every week.

## What Spaw answers

`block_pooled` is true when the number's code is pooled, false when it is not, and null when no allocated block or code answers, as for an unassigned block, and outside the NANPA and CNAC tables. In a pooled US code, `carrier`, `carrier_code`, `carrier_brand`, a `line_type` the holder settles and `is_virtual` describe the holder of the number's own thousands-block, and `block_assigned_at` is the day NANPA assigned that block. A block the report lists as available (AV or AP) answers [`unassigned_block`](/docs/reasons/unassigned_block) while the copy is fresh. A block still partly in use by its former holder, or available only from a future date, keeps the code holder's answer, and so does every Canadian code, which is read at code level. A retained block carries no date, so `block_assigned_at` is null there. So is the date of 112,611 of the 197,177 US codes (57.1%) in NANPA's tables of 26 September 2026, including every code assigned before 2001, because NANPA dates none earlier: a null does not mean new.

## What it does not mean

A thousands-block is an allocation, like the code around it: it names who NANPA assigned the numbers to, not who serves one of them after a [port](/glossary/number-portability). Pooling is not a risk signal either. `block_pooled` carries no weight; it says only that the number's code is pooled, not whether the block or the code answered. The state pages linked from [the United States phone facts](/tools/phone-number-lookup/countries/us) count the pooled codes of every area code.

Reference: https://spaw.co/glossary/number-pooling