per cubic foot
The reciprocal cubic foot counts items per cubic foot of volume, and equals about 35.3147 reciprocal cubic metres. The ratio is exact as a fraction, since the international foot is exactly 0.3048 metres and a cubic foot exactly 0.028316846592 cubic metres, but the decimal value shown here is rounded because the reciprocal does not terminate. It survives in North American cleanroom and air filtration practice, where the older Federal Standard 209E classes counted particles per cubic foot.
Watch out: The old US cleanroom classes such as Class 100 or Class 1000 are counts of particles 0.5 micrometres and larger per cubic foot. The ISO 14644 classes that replaced them count per cubic metre, so Class 100 corresponds to ISO 5 rather than to any round metric number.
| 1 ft⁻³ (Number density) | 35.314667 m⁻³ |
| 1 $/ft³ (Cost per volume) | 35.314667 $/m³ |
Cost per cubic foot. The conversion to cost per cubic metre is exact, since the international foot is exactly 0.3048 metres and a cubic foot exactly 0.028316846592 cubic metres, and it touches only the volume: one currency unit per cubic foot is about 35.31 per cubic metre in the same currency.