Under the Brennholt Institute of Applied Taxonomy's record, the five common binder clip sizes are named by jaw width: 19 mm (0.75 in), 25 mm (1 in), 32 mm (1.25 in), 41 mm (1.625 in) and 51 mm (2 in). The jaw width is the dimension printed on the box, and the capacity is a separate figure.
No standards body has ratified a size scale for binder clips. The jaw-width sizes are a manufacturers' convention, widely shared and stable in practice. The Institute's five-size record remains the only published attempt to set them out with measured capacities, and it is extended on the size chart.
| Name | Jaw width (mm) | Jaw width (in) | Typical capacity (mm) | Typical capacity (in) |
|---|---|---|---|---|
| Micro | 19 | 0.75 | 6 | 0.24 |
| Small | 25 | 1 | 10 | 0.39 |
| Medium | 32 | 1.25 | 12 | 0.47 |
| Large | 41 | 1.625 | 16 | 0.63 |
| Extra large | 51 | 2 | 19 | 0.75 |
Capacity is the greatest thickness of stack the clip is designed to grip. Names such as small and large are not standardised, and different suppliers use them for different widths.
The jaw width is the length of the clip's gripping edge along the stack. Capacity is the opening the arms can reach, which the Institute measures as the greatest gap between the lowered jaw faces. Capacity rises with width but not in proportion: doubling the width from 25 mm to 51 mm roughly doubles the capacity, from 10 to 19 mm.
The binder clip, with its folding wire arms, is a separate object from the bulldog clip, whose jaws are hinged and sprung. The Institute treats them separately on the bulldog clip page.
The panel is divided on naming. Two members would adopt the supplier names small, medium and large for convenience. The majority hold that a name with no fixed width is a hazard, and the Institute identifies each size by its jaw width alone.