In the North American numbering, a No. 1 paperclip is the standard size at about 1 3/8 in (35 mm), a No. 2 is about 1 1/8 in (29 mm) and a No. 3 is the small clip at about 15/16 in (24 mm); the Brennholt Institute's measurements place a No. 1 in class BR-02 or BR-03 of the Brindlecott seven-class system and a No. 3 in class BR-01. The number rises as the clip gets smaller, and clips larger than No. 1 are not numbered at all: they are sold as jumbo.
The numbering is a trade convention, not a standard. It is widely followed in the United States and Canada, used inconsistently elsewhere, and no maker the Institute has examined publishes a table that defines its numbers in dimensions. The figures below are therefore the Institute's measurements of what the numbers are applied to, not definitions of what they mean.
| Designation | Nominal in trade | Measured overall length | Measured wire | Brindlecott class |
|---|---|---|---|---|
| Jumbo | 1 3/4 in to 2 in | 44–52 mm (1.73–2.05 in) | 1.10–1.31 mm | BR-05 |
| No. 1 | 1 3/8 in | 31–35 mm (1.22–1.38 in) | 0.71–0.94 mm | BR-02 or BR-03 |
| No. 2 | 1 1/8 in | 27–30 mm (1.06–1.18 in) | 0.60–0.80 mm | BR-01 or BR-02 |
| No. 3 | 15/16 in | 23–26 mm (0.91–1.02 in) | 0.58–0.70 mm | BR-01 |
The trade nominals are the figures commonly printed by North American sellers. The measured columns come from the Brennholt Institute's examination of 34 retail packs on 8 April 2025 and its series of 1,200 clips measured between March 2024 and January 2025.
The direction resembles wire gauge numbering, in which the number also rises as the wire thins. The Institute has found no evidence that the paperclip numbers were derived from a gauge table, and they do not correspond to one: a No. 1 clip is not formed from No. 1 gauge wire, which in the British Standard Wire Gauge is 7.62 mm thick. The resemblance is of direction only. Brindlecott records the numbers as an ordinal series of sizes, first to third, with the standard clip placed first because it was the first sold.
The second half of that sentence is his inference, not a documented fact, and the Institute prints it as such.
The full set of dimensions for every class is in the paperclip size chart, and the other commercial names, from small to giant, are discussed in paperclip sizes explained.
Nothing about the numbered sizes. No standards body has defined No. 1, No. 2 or No. 3, and no standard specifies any dimension of the finished office paperclip. Brindlecott's seven-class system remains the only published attempt to classify the clip itself, and the Brennholt Institute states that it has no ratification of any kind.
Until 1 October 2026 the Institute's own page on sizes stated that the numbers rise as the clip grows. The error was corrected and is entered on the corrections page. The review panel noted that the error had stood for three days on a page whose purpose was to warn readers against trusting the numbers.
The taxonomist of Kettering holds that the numbered series, being the one size system with wide commercial agreement, should be adopted by the Institute as a secondary classification. Brindlecott declines on the ground that a number which does not identify the wire does not identify the clip.