SI-compliant Expressions
SI-compliant units that can be used as alternatives are shown in the chart below. Expressions that the BIPM does not explicitly recognize as being suitable for denoting dimensionless quantities with the SI are shown in underlined green text.
| NOTATIONS FOR DIMENSIONLESS QUANTITIES | ||||
|---|---|---|---|---|
| Measure | SI units |
Named parts-per ratio |
Parts-per abbreviation or symbol |
Value in scientific notation |
| A strain of… | 2 cm/m | 2 parts per hundred | 2% | 2 × 10−2 |
| A sensitivity of… | 2 mV/V | 2 parts per thousand | 2 ‰ | 2 × 10−3 |
| A sensitivity of… | 0.2 mV/V | 2 parts per ten thousand | 2 ‱ | 2 × 10−4 |
| A sensitivity of… | 2 µV/V | 2 parts per million | 2 ppm | 2 × 10−6 |
| A sensitivity of… | 2 nV/V | 2 parts per billion | 2 ppb | 2 × 10−9 |
| A sensitivity of… | 2 pV/V | 2 parts per trillion | 2 ppt | 2 × 10−12 |
| A mass fraction of… | 2 mg/kg | 2 parts per million | 2 ppm | 2 × 10−6 |
| A mass fraction of… | 2 µg/kg | 2 parts per billion | 2 ppb | 2 × 10−9 |
| A mass fraction of… | 2 ng/kg | 2 parts per trillion | 2 ppt | 2 × 10−12 |
| A mass fraction of… | 2 pg/kg | 2 parts per quadrillion | 2 ppq | 2 × 10−15 |
| A volume fraction of… | 5.2 µL/L | 5.2 parts per million | 5.2 ppm | 5.2 × 10−6 |
| A mole fraction of… | 5.24 µmol/mol | 5.24 parts per million | 5.24 ppm | 5.24 × 10−6 |
| A mole fraction of… | 5.24 nmol/mol | 5.24 parts per billion | 5.24 ppb | 5.24 × 10−9 |
| A mole fraction of… | 5.24 pmol/mol | 5.24 parts per trillion | 5.24 ppt | 5.24 × 10−12 |
| A stability of… | 1 (µA/A)/min. | 1 part per million per min. | 1 ppm/min. | 1 × 10−6/min. |
| A change of… | 5 nΩ/Ω | 5 parts per billion | 5 ppb | 5 × 10−9 |
| An uncertainty of… | 9 µg/kg | 9 parts per billion | 9 ppb | 9 × 10−9 |
| A shift of… | 1 nm/m | 1 part per billion | 1 ppb | 1 × 10−9 |
| A strain of… | 1 µm/m | 1 part per million | 1 ppm | 1 × 10−6 |
| A temperature coefficient of… | 0.3 (µHz/Hz)/°C | 0.3 part per million per °C | 0.3 ppm/°C | 0.3 × 10−6/°C |
| A frequency change of… | 0.35 × 10−9 ƒ | 0.35 part per billion | 0.35 ppb | 0.35 × 10−9 |
Note that the notations in the “SI units” column above are all dimensionless quantities; that is, the units of measurement factor out in expressions like “1 nm/m” (1 nm/m = 1 nano = 1 × 10−9) so the quotients are pure-number coefficients with values less than 1.
Read more about this topic: Parts-per Notation
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