| Micrograms (μg) | Long tons (t) |
|---|---|
| 1 Microgram | 9.84206527611 × 10-13 t |
| 2 Micrograms | 1.96841305522 × 10-12 t |
| 3 Micrograms | 2.95261958283 × 10-12 t |
| 4 Micrograms | 3.93682611044 × 10-12 t |
| 5 Micrograms | 4.92103263806 × 10-12 t |
| 10 Micrograms | 9.84206527611 × 10-12 t |
| 20 Micrograms | 1.96841305522 × 10-11 t |
| 25 Micrograms | 2.46051631903 × 10-11 t |
| 50 Micrograms | 4.92103263806 × 10-11 t |
| 100 Micrograms | 9.84206527611 × 10-11 t |
| Reference | Micrograms (μg) | Long tons (t) |
|---|---|---|
| A sheet of A4 paper (80 gsm) | 5000000 μg | 0.00000492103 t |
| One litre of water | 1 × 109 μg | 0.000984207 t |
| Average adult human | 7 × 1010 μg | 0.0688945 t |
| A small car | 1.4 × 1012 μg | 1.37789 t |
The microgram is a unit of mass equal to one millionth of a gram, or one thousandth of a milligram. Its official symbol is µg, written with the Greek letter mu.
In medicine that symbol is a known hazard. Handwritten, µg is easily read as mg, a thousandfold error, and the mistake has killed patients. Safety bodies including the Institute for Safe Medication Practices therefore recommend writing mcg instead on prescriptions and labels, and most hospital systems now enforce it. The abbreviation is not SI and would be wrong in a scientific paper, but it is the safer choice on a drug chart.
Micronutrients live at this scale. Vitamin B12, folate, iodine, selenium, biotin and vitamin K are all dosed in micrograms, and daily requirements run from a few micrograms to a few hundred. Vitamin D is given either in micrograms or in international units, with one microgram equal to forty IU, a dual convention that causes constant confusion on supplement labels. Potent drugs use the unit too: fentanyl, levothyroxine, digoxin and most hormonal contraceptives are dosed in micrograms rather than milligrams.
Air quality reporting has made the microgram familiar to the public. Fine particulate matter is measured in micrograms per cubic metre, and the World Health Organization guideline for annual PM2.5 exposure is five micrograms per cubic metre. Nitrogen dioxide, sulphur dioxide and ozone limits are written the same way, so the number quoted in a news report about pollution is almost always a count of micrograms in a cubic metre of air.
Toxicology works here because potency and hazard both scale with dose. Digoxin is prescribed in a few hundred micrograms a day and becomes dangerous not far above that, thyroid hormone is dispensed in 25-microgram steps, and the opioid fentanyl is active at doses of tens of micrograms, which is why illicitly mixed powders containing it are so often lethal. Analytical chemistry meets the unit from the other direction: modern instruments detect pesticides, metals and pharmaceuticals in water at concentrations of micrograms per litre, and regulatory limits are written at that level. A microgram is invisible, weighs less than a speck of dust, and yet is the natural unit for both the dose that heals and the dose that kills.
One microgram equals 0.001 milligrams, one millionth of a gram, and one thousand nanograms.
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.