Convert t to g

A tonne is 1,000 kilograms, and it is not the same as either the US short ton (907 kg) or the UK long ton (1,016 kg). Where the difference matters, this one is sometimes written "metric ton".

Grams are the unit of recipes and postage outside the United States, and the unit nutrition labels use nearly everywhere.

Going from tonnes to grams moves the decimal point 6 places to the right and changes nothing else. There is no factor to remember and no rounding to decide: the digits stay in the same order and only their position changes.

1,234 t is 1234000000 g — same digits, moved along. That is worth knowing because it is the one kind of conversion you can check at a glance: if the digits of the answer are not the digits you started with, something other than the conversion has happened to them.

This page uses the metric tonne, which here is 1000000 g. The US short ton is 907184.74 g, 9.3 % lighter; the UK long ton is 1016046.9088 g, 1.6 % heavier. Three units, one letter between two of their names.

Where the figure came from usually settles which one it is: tonnes for shipping, freight and emissions nearly everywhere, short tons in American industry, long tons in older British sources. Write "metric ton" where it has to be unambiguous — of the three it is the only name that cannot be read as one of the others.

The whole value of this conversion is the identity it produces. A tonne is a million grams, so one gram in a tonne is one part in a million by mass — and because a milligram is a thousandth of a gram and a kilogram a thousand of them, one milligram per kilogram is the same concentration written at a different scale. Three notations, one number, no conversion factor between them.

That is worth holding because different industries picked different ones. Mining says grams per tonne, food and environmental regulation say milligrams per kilogram, and general chemistry says parts per million. A specification quoting 5 mg/kg and an assay reporting 5 g/t are stating the identical thing, and a report that converts between them and gets a different number has made an arithmetic error rather than a unit one.

Nothing about this pair is really about how heavy a tonne is. The figure appears as the bottom half of a ratio — grams of gold per tonne of ore, grams of additive per tonne of feed, grams of a residue per tonne of product — and the reader wants to know what a small number sitting on top of it means in practice.

It also explains why the numbers look so small and matter so much. A grade of 1 g/t is one part per million and is an economic ore body at scale; a contaminant at 1 mg/kg is one part per million and may be a regulatory breach. The same concentration is a business and a hazard depending on what the gram is made of, and the tonne underneath is doing nothing but making the fraction readable.

Gold grades are quoted in single-digit grams per tonne, and the arithmetic of why that works runs through this conversion. A tonne of rock containing five grams of gold contains five parts per million of it; move a few million tonnes of rock a year and the grams add up to a production figure in tonnes of metal.

The historic American unit for the same thing was troy ounces per short ton, and it converts at 34.2857 g/t per ounce — a factor with two ambiguities folded into it, because both the ounce and the ton are the unusual ones. A grade quoted as 0.15 opt is about 5.1 g/t, and reading it as ordinary ounces or as metric tonnes gets a different answer each time.

Animal feed, fertiliser blends, polymer masterbatch and water treatment all specify at grams per tonne, because that is the scale at which the mixing actually happens. A dose of 200 g/t is 200 ppm, and on a five-tonne batch it is a kilogram of material weighed out on an ordinary scale — a number a person can handle, derived from a concentration a person cannot.

The failure mode is a batch size that is not the batch size the specification assumed. A dose written per tonne applied to a 500 kg batch needs halving, and the error is silent because both figures look reasonable. Convert the batch to the same unit as the specification before doing anything else; the conversion is a decimal point and the mistake it prevents is a factor of two.

A million is the kind of number that survives being typed wrong. 1,000,000 g and 100,000 g look similar at a glance and are a tenth of each other, and a concentration derived from the second is out by a factor of ten in a way that nothing downstream will flag — 50 g/t and 5 g/t are both plausible grades.

The defences are the ones any large factor deserves. Write the tonne figure in kilograms as an intermediate, because 1,000 kg is easier to verify than 1,000,000 g. Prefer the mg/kg form when the numbers are small, since it keeps both sides of the ratio in three digits. And where a document has to carry the raw figure, scientific notation is a courtesy rather than an affectation.

A grams-per-tonne figure is not the result of weighing a tonne. It comes from taking a sample of a few hundred grams, assaying that, and scaling the result to a tonne — so the accuracy of the answer is set by how representative the sample was, not by any scale.

That is why the same material can return different grades from different laboratories and why sampling protocol is the part of the process with the standards attached to it. The conversion between the tonne and the gram contributes no error at all, being exact by definition. Every uncertainty in the final number entered before the units were involved.

Regulatory limits for heavy metals, pesticide residues and contaminants are written in milligrams per kilogram, which this conversion shows is the same as grams per tonne. A limit of 0.1 mg/kg is 0.1 g/t, and expressing it that way makes the industrial scale legible: a hundred grams of the substance spread through a thousand tonnes of product would breach it.

Water is the one place the equivalence needs care. Limits in water are often given per litre rather than per kilogram, and a litre of water weighs a kilogram closely enough that mg/l and mg/kg are used interchangeably — for water. For anything denser or lighter than water the two diverge by the density, and a conversion that ignores that is wrong by however much the substance is not water.