| Nanograms (ng) | Ounces (oz) |
|---|---|
| 1 Nanogram | 3.52739619496 × 10-11 oz |
| 2 Nanograms | 7.05479238992 × 10-11 oz |
| 3 Nanograms | 1.05821885849 × 10-10 oz |
| 4 Nanograms | 1.41095847798 × 10-10 oz |
| 5 Nanograms | 1.76369809748 × 10-10 oz |
| 10 Nanograms | 3.52739619496 × 10-10 oz |
| 20 Nanograms | 7.05479238992 × 10-10 oz |
| 25 Nanograms | 8.8184904874 × 10-10 oz |
| 50 Nanograms | 0.00000000176369809748 oz |
| 100 Nanograms | 0.00000000352739619496 oz |
| Reference | Nanograms (ng) | Ounces (oz) |
|---|---|---|
| A sheet of A4 paper (80 gsm) | 5 × 109 ng | 0.17637 oz |
| One litre of water | 1 × 1012 ng | 35.274 oz |
| Average adult human | 7 × 1013 ng | 2469.18 oz |
| A small car | 1.4 × 1015 ng | 49383.5 oz |
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 ounce is a unit of mass equal to one sixteenth of an avoirdupois pound, or exactly 28.349523125 grams. Its symbol is oz, from the Italian onza. It is the everyday small weight of the United States and remains in common use in the United Kingdom alongside metric units.
There are several ounces, and confusing them is easy. The avoirdupois ounce described here is the one used for food and general goods. The troy ounce, used for gold, silver and platinum, is about 31.103 grams, some ten per cent heavier, which is why a troy pound of twelve ounces weighs less than an avoirdupois pound of sixteen. The fluid ounce is not a mass at all but a volume, and the imperial and US fluid ounces differ from each other by about four per cent.
American food packaging is built on the ounce. Net weights appear in ounces below sixteen and in pounds and ounces above, and recipe quantities for cheese, chocolate, pasta and meat are given the same way. Postal rates for letters step in ounces, and boxing, wrestling and other weight-class sports state limits in pounds and ounces.
The word comes from the Latin uncia, meaning a twelfth part, which is also the ancestor of the inch. That original twelfth survives in the troy ounce but not in the avoirdupois one, whose sixteenth-of-a-pound relationship came later from the wool trade of medieval Europe. Two units with the same name and different arithmetic is the direct result.
Precious metals are the other ounce's territory. Gold, silver, platinum and palladium are priced per troy ounce of 31.1035 grams, about ten per cent heavier than the avoirdupois ounce used for groceries, and every quoted bullion price in the world refers to it. A one-ounce gold coin is therefore heavier than an ounce of butter, and a bar described as a kilogram contains 32.15 troy ounces rather than 35.27 ordinary ones. The troy system also keeps its own subdivisions, with 20 pennyweights to the ounce, which is why a jeweller's scale and a kitchen scale are calibrated differently even when both are marked in ounces.
One ounce equals 28.349523125 grams exactly, one sixteenth of a pound, or 437.5 grains.