Convert t to oz

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".

An ounce is a sixteenth of a pound. It is not the fluid ounce, which measures volume, and the two are only loosely related — a fluid ounce of water weighs about an ounce, which is where the name came from and where the confusion starts.

The factor is 35273.96195, and almost nobody carries that around. Rounded to 35000 it is off by 0.78 % — which stays invisible on small numbers and turns into a whole unit somewhere around 1,000 t.

That is the number worth knowing before you round: not the error itself, but where it stops being ignorable. Below that point the shorter factor is the sensible one; above it, use the field above, which never rounds until it prints.

This page uses the metric tonne, which here is 35273.96195 oz. The US short ton is 32000 oz, 9.3 % lighter; the UK long ton is 35840 oz, 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 ounce has been defined in metric terms since the international yard and pound agreement of 1959, and in this page's units that comes out at 0.0000283495231 t to one. The definition is exact by stipulation — it was not measured, and it cannot be refined by measuring it better. The decimal above is not the whole of it, though: this page stops at nine significant digits and the ratio carries on past them.

Before that agreement the US and the British versions differed slightly, and old survey figures still carry the older definition. For anything outside land surveying the difference is far below the precision anybody is working to.

The field above converts avoirdupois ounces, the sixteenth of a pound used for everything that is not a precious metal, and it gives 35,273.9619 to the tonne. Metal is counted in troy ounces of 31.1034768 g, and a tonne holds 32,150.7466 of those. The gap is 9.7 per cent in the size of the unit and 8.8 per cent in the count, and nothing in how either is written distinguishes them.

Both numbers are exact rather than measured. The tonne is a thousand kilograms by definition, the avoirdupois ounce is a sixteenth of a pound of exactly 0.45359237 kg, and the troy ounce is 480 grains of exactly 64.79891 mg each. Nobody weighed anything to arrive at either figure, which is why they can be quoted to as many digits as a document needs.

Gold, silver, platinum and palladium are quoted per troy ounce, always, with no qualifier — a headline price "per ounce" is a troy ounce and the market assumes you know. Base metals go the other way entirely: copper, aluminium and zinc trade per tonne on the London exchange and per pound in the United States, and the ounce never appears.

So the direction of this conversion tells you something about what is being converted. Tonnes into ounces is nearly always a precious metal, which means the answer wanted is nearly always troy. Where the material is industrial and somebody has asked for ounces anyway, the avoirdupois figure above is the right one, and it is worth writing "oz" against one and "ozt" against the other so the next reader does not have to guess.

Mining companies report output in tonnes of ore and in ounces of metal in the same document, because the two numbers serve different readers: the tonnage is an operational figure and the ounce count is what is sold. A grade in grams per tonne, a throughput in tonnes and a recovery percentage multiply into an ounce figure, and this conversion is the last step of that chain.

Central bank and national reserve figures run the same way. Holdings are commonly published in tonnes and valued in troy ounces, so a reserve of 100 tonnes is 3,215,075 troy ounces before anything is priced. Converting with the ordinary ounce inflates that count by more than a quarter of a million ounces, which is the kind of error that is only obvious once the valuation comes out wrong.

The avoirdupois figure earns its place whenever a tonne of something is being counted into retail units. American packaging is sized in ounces — 8 oz, 12 oz, 16 oz — so a production run measured in tonnes converts directly into a number of packs. A tonne divided into 12 oz units gives 2,939 of them, with a few hundred grams left over.

It is also the right unit for anything where the ounce is a portion rather than a commodity: servings, doses by weight, sample sizes. In those cases the tonne is the odd unit in the sentence and the ounce is the familiar one, which is the reverse of the precious-metals case and a good reason to state which ounce is meant even when it seems obvious.

A tonne quoted to the nearest tonne converts to an ounce count with four figures of meaning and three of decoration. 12 t is 423,287.54 oz, and the trailing digits are arithmetic rather than information — the input claimed nothing finer than a tonne, which is 35,274 ounces of slack on its own.

The rule is the ordinary one and it is unusually visible here because the factor is so large: a conversion cannot add precision, and a big multiplier makes the false precision spectacular. Report the ounce figure to about the same number of significant digits the tonne figure had, and keep the full-precision number only where it will be multiplied by a price and rounded at the end.

Troy weight does not stop at the ounce, and the divisions below it are not the ones the ordinary ounce uses. A troy ounce is 20 pennyweight, and a pennyweight is 24 grains, making 480 grains to the ounce. The grain itself is exactly 64.79891 mg and is the one unit the troy and avoirdupois systems share — an avoirdupois pound is 7,000 grains and a troy pound is 5,760.

That shared grain is why the two systems can be compared exactly at all, and it is also why a troy pound is lighter than an ordinary pound while a troy ounce is heavier: there are twelve troy ounces to the troy pound and sixteen ordinary ounces to the ordinary one. Anything quoted in pennyweight or grains — jewellery scrap, assay results — is troy, whatever the ounce beside it is called.

The conversion of the price runs opposite to the conversion of the mass: more ounces per tonne means fewer currency units per ounce. A price of 1,000 per troy ounce is 32,150,747 per tonne; a price of 40,000 per tonne is 1.244 per troy ounce. Divide by 32,150.7466 in one direction and multiply by it in the other.

The trap is mixing the two ounces inside one comparison. A refiner quoting per tonne and a market quoting per troy ounce are directly comparable only through the troy figure, and using 35,274 makes the per-tonne price look about nine per cent cheaper than it is. Where two quotes are close, that error alone decides between them.