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.
| Unit | Symbol | 1 Nanogram equals | 1 of these equals | Converter |
|---|---|---|---|---|
| Microgram | μg | 0.001 μg | 1000 ng | Nanograms to Micrograms |
| Milligram | mg | 0.000001 mg | 1000000 ng | Nanograms to Milligrams |
| Gram | g | 0.000000001 g | 1000000000 ng | Nanograms to Grams |
| Kilogram | kg | 1 × 10-12 kg | 1000000000000 ng | Nanograms to Kilograms |
| Tonne | t | 1 × 10-15 t | 1 × 1015 ng | Nanograms to Tonnes |
| Grain | gr | 0.0000000154323583529 gr | 64798910 ng | Nanograms to Grains |
| Dram | dr | 5.64383391193 × 10-10 dr | 1771845195.31 ng | Nanograms to Drams |
| Ounce | oz | 3.52739619496 × 10-11 oz | 28349523125 ng | Nanograms to Ounces |
| Pound | lb | 2.20462262185 × 10-12 lb | 453592370000 ng | Nanograms to Pounds |
| Stone | st | 1.57473044418 × 10-13 st | 6350293180000 ng | Nanograms to Stones |
| Hundredweight | cwt | 1.96841305522 × 10-14 cwt | 50802345440000 ng | Nanograms to Hundredweights |
| Long ton | t | 9.84206527611 × 10-16 t | 1.0160469088 × 1015 ng | Nanograms to Long tons |