| Long tons (t) | Nanograms (ng) |
|---|---|
| 1 Long ton | 1.0160469088 × 1015 ng |
| 2 Long tons | 2.0320938176 × 1015 ng |
| 3 Long tons | 3.0481407264 × 1015 ng |
| 4 Long tons | 4.0641876352 × 1015 ng |
| 5 Long tons | 5.080234544 × 1015 ng |
| 10 Long tons | 1.0160469088 × 1016 ng |
| 20 Long tons | 2.0320938176 × 1016 ng |
| 25 Long tons | 2.540117272 × 1016 ng |
| 50 Long tons | 5.080234544 × 1016 ng |
| 100 Long tons | 1.0160469088 × 1017 ng |
| Reference | Long tons (t) | Nanograms (ng) |
|---|---|---|
| A sheet of A4 paper (80 gsm) | 0.00000492103 t | 5 × 109 ng |
| One litre of water | 0.000984207 t | 1 × 1012 ng |
| Average adult human | 0.0688945 t | 7 × 1013 ng |
| A small car | 1.37789 t | 1.4 × 1015 ng |
The long ton is a unit of mass equal to 2240 pounds, or about 1016.047 kilograms. It is the ton of the British imperial system, sometimes called the imperial ton or the gross ton, and it sits within one and a half per cent of the metric tonne, which is both convenient and a persistent source of error.
Three tons compete for the same word. The long ton is 2240 pounds, the short or American ton is 2000 pounds, and the tonne is 1000 kilograms, roughly 2204.6 pounds. The long ton and the tonne differ by about sixteen kilograms, small enough to be invisible in a rough estimate and large enough to matter across a shipload. Contracts, customs declarations and commodity quotations therefore name the ton explicitly rather than relying on context.
Its structure follows the rest of the imperial system: twenty hundredweight of 112 pounds each. That is where the 2240 comes from, and it makes the long ton the natural top of a chain running pound, stone, hundredweight, ton, each step a whole number of the last.
British shipping, mining and steel used it for well over a century, and it survives in some maritime contexts and in older engineering literature. The displacement of warships is still often quoted in long tons, which is why published figures for historic vessels can differ by a couple of per cent depending on which ton the source used.
Shipping complicates the word further by using ton for things that are not masses at all. A register ton is a hundred cubic feet of enclosed space, used to size a vessel for harbour dues; a freight ton may be a mass or a volume, whichever yields the larger charge; and displacement, the figure by which warships are described, is the mass of water a hull pushes aside, historically stated in long tons. Reading a ship's particulars therefore means checking which ton is meant before comparing anything. Deadweight tonnage, the cargo, fuel and stores a ship can carry, is a mass and is now given in metric tonnes, but older registers state it in long tons.
One long ton equals 2240 pounds, about 1016.047 kilograms, or 1.12 short tons.
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.