Paperclip sizes are commercial designations. They are set by each maker, they differ between makers, and no body arbitrates them. A clip sold as No. 1 by one supplier can be the same object as a clip sold as No. 2 by another, and both may be described as 32 mm. The number on the box records what the seller calls the product, not what the product is.
The Brennholt Institute of Applied Taxonomy records commercial designations as observations and classifies clips by measured wire diameter instead. This page sets out what the designations correspond to in practice, with the measured ranges behind each.
| Designation seen on packaging | Overall length observed | Wire diameter observed | Usual class |
|---|---|---|---|
| Small, No. 1, 26 mm, 28 mm | 25–29 mm | 0.58–0.72 mm | BR-01 |
| Standard, No. 2, 32 mm, 33 mm | 31–34 mm | 0.71–0.94 mm | BR-02 or BR-03 |
| Large, No. 3, 40 mm, 41 mm | 38–42 mm | 0.95–1.16 mm | BR-04 |
| Extra large, No. 4, 50 mm | 48–52 mm | 1.16–1.31 mm | BR-05 |
| Giant, jumbo | 50–78 mm | 1.10–1.31 mm | BR-05 |
Two features of the table matter more than the numbers in it. The overall-length ranges overlap barely, so a length designation is a fair guide to length. The wire-diameter ranges overlap heavily, and the Standard row spans two full classes. A buyer choosing by designation is choosing a length reliably and a stiffness not at all.
This is the single most consequential fact on the page. Holding capacity is governed by wire diameter, and a clip sold as 32 mm may be class BR-02, holding 12 sheets, or class BR-03, holding 18. Two boxes both marked 32 mm, examined by the Institute on 8 April 2025, differed in wire diameter by 0.19 mm — a difference of 50 per cent in capacity, invisible on the packaging.
Of the 34 retail packs the Institute examined that day, none printed a wire diameter and none printed a gauge number. All printed an overall length.
Numbered designations — No. 1 through No. 4, and occasionally No. 5 and No. 6 — run in the opposite direction to wire gauge systems: the number rises as the clip gets larger. They are not gauge numbers and should not be converted as if they were. The Institute has found no maker publishing a table that defines its own numbered series in dimensions, and no two sellers whose numbered series were demonstrably identical.
Length in millimetres is the most useful designation available to a buyer, and it is close to reliable: observed overall lengths fell within 2 mm of the printed figure in 31 of the 34 packs examined. The three exceptions were all printed 32 mm and measured 29, 30 and 35 mm. The Institute treats a printed millimetre figure as accurate to ±2 mm and says so.
A buyer who needs a defined object should specify wire diameter in millimetres, because it is the property that determines capacity and stiffness, and because it is the only property that can be verified on arrival with a caliper. The Institute suggests the form 0.90 mm wire, 34 mm overall rather than No. 2 or standard. No supplier is obliged to answer, since no standard requires the figure to be published, and the Institute records that it has no evidence of any supplier doing so.
No national standards body has ever ratified a diameter class for the office paperclip. Brindlecott's seven-class system remains the only published attempt, and it exists because the commercial designations described on this page do not classify anything.
The Institute's review panel objected on 3 March 2026 to the usual class column, on the ground that assigning a class to a commercial designation lends the designation a precision it does not have, and that the column will be quoted in isolation from the overlap it is meant to expose. Brindlecott retained the column and added the overlap ranges beside it. The panel has not withdrawn the note.
The taxonomist of Kettering holds that overall length, being the one figure makers do print and broadly honour, should be the Institute's primary classifying property on grounds of usefulness. Brindlecott's answer is that a classification built on the property a seller chooses to disclose is a catalogue, not a taxonomy. Neither has published since 2025.