| Nanograms (ng) | Pounds (lb) |
|---|---|
| 1 Nanogram | 2.20462262185 × 10-12 lb |
| 2 Nanograms | 4.4092452437 × 10-12 lb |
| 3 Nanograms | 6.61386786555 × 10-12 lb |
| 4 Nanograms | 8.8184904874 × 10-12 lb |
| 5 Nanograms | 1.10231131092 × 10-11 lb |
| 10 Nanograms | 2.20462262185 × 10-11 lb |
| 20 Nanograms | 4.4092452437 × 10-11 lb |
| 25 Nanograms | 5.51155655462 × 10-11 lb |
| 50 Nanograms | 1.10231131092 × 10-10 lb |
| 100 Nanograms | 2.20462262185 × 10-10 lb |
| Reference | Nanograms (ng) | Pounds (lb) |
|---|---|---|
| A sheet of A4 paper (80 gsm) | 5 × 109 ng | 0.0110231 lb |
| One litre of water | 1 × 1012 ng | 2.20462 lb |
| Average adult human | 7 × 1013 ng | 154.324 lb |
| A small car | 1.4 × 1015 ng | 3086.47 lb |
The nanogram is a unit of mass equal to one billionth of a gram, or a thousandth of a microgram. Its symbol is ng. Expressed in the base unit of the SI it is 10 raised to the power minus twelve kilograms.
Nothing historical stands behind the nanogram. It exists because SI prefixes extend without limit, and it became useful only when instruments grew sensitive enough to justify it. A good analytical balance resolves tenths of a microgram and stops there; no balance weighs a nanogram directly. The quantity is instead inferred, from the signal a mass spectrometer, an immunoassay or a chromatography column produces when a known volume of sample passes through it.
Clinical laboratories are where most people meet the unit without noticing. Hormone and drug concentrations in blood are reported in nanograms per millilitre: testosterone, prostate-specific antigen, digoxin, tacrolimus, and vitamin D in American practice. Therapeutic drug monitoring depends on the scale, because the difference between an effective and a toxic concentration of some drugs is a few nanograms per millilitre. Anti-doping thresholds are written the same way, which is why an athlete can test positive for a substance present in quantities invisible by any other measure.
Environmental chemistry uses it for the most toxic contaminants, where the interesting concentrations are far below anything a gram-scale unit describes comfortably. Dioxins and furans in air are reported in nanograms per cubic metre, mercury and polycyclic aromatic hydrocarbons in nanograms per litre of water. Regulatory limits for these substances are set at concentrations that only became measurable in the second half of the twentieth century, so the unit and the regulation arrived together.
The scale is hard to picture. A single grain of fine table salt weighs roughly sixty micrograms, which is sixty thousand nanograms. A typical mammalian cell weighs on the order of one nanogram, so a nanogram of tissue is a handful of cells. A microgram of anything is already invisible; a nanogram is a thousandth of that.
One nanogram equals 0.001 micrograms, one millionth of a milligram, and one billionth of a gram.
The pound is a unit of mass equal to exactly 0.45359237 kilograms. Its symbol is lb, from the Latin libra, and the plural is sometimes written lbs. It is the principal unit of mass in the United States and remains widely used in the United Kingdom for body weight and food.
That exact value dates from the International Yard and Pound Agreement of 1959, in which the United States, the United Kingdom, Canada, Australia, New Zealand and South Africa agreed a single definition for both units. Before it, the American and British pounds differed slightly, which was tolerable in commerce and unacceptable in engineering as aircraft and munitions were built to shared drawings. Defining the pound in terms of the kilogram, rather than the other way round, quietly made the imperial system a derivative of the metric one.
The abbreviation lb is a reminder of the Roman libra pondo, a pound by weight, from which English took the word pound and the symbol from different halves of the phrase. The same libra gave the pound sterling its name and its old symbol, which is why a currency and a weight share a word.
Everyday American life is dense with the unit. Body weight, groceries sold loose, meat, flour and sugar, freight, and gym equipment are all in pounds. Weight-class sports set limits in pounds, and infant birth weights are given in pounds and ounces. In the United Kingdom the pound survives socially rather than commercially: shops sell in kilograms while people still describe their own weight in stones and pounds.
A second pound causes endless trouble in engineering. The pound-force is the weight of one pound of mass in standard gravity, about 4.448 newtons, and it is written with the same abbreviation in most American practice. Since force equals mass times acceleration, using the two interchangeably requires a conversion constant, and generations of textbooks have handled that either by introducing the slug — the mass that one pound-force accelerates at one foot per second squared, about 14.59 kilograms — or by carrying a factor of 32.174 through every calculation. Neither is elegant, and the confusion is the strongest practical argument the metric system has ever had in its favour.
One pound equals 0.45359237 kilograms exactly, 16 ounces, or 7000 grains.