Convert kg to t

The kilogram was the last unit defined by a physical object — a cylinder in a vault near Paris that was slowly losing mass. Since 2019 it has been fixed to the Planck constant instead.

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".

Going from kilograms to tonnes moves the decimal point 3 places to the left 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 kg is 1.234 t — 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 1000 kg. The US short ton is 907.18474 kg, 9.3 % lighter; the UK long ton is 1016.04691 kg, 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 SI symbol for the tonne is a lowercase t, and it is one of the few unit symbols where the case genuinely carries meaning: an uppercase T is the tesla, the unit of magnetic flux density. Beyond SI the abbreviations multiply — MT, mt, tn, and the bare word "ton" — and none of them is defined tightly enough to travel between industries without an explanation.

The practical rule for anything leaving your own desk is to write the number in kilograms as well, or to spell out "metric ton". A quotation reading "4.27 t (4,270 kg)" cannot be misread by anybody, costs six characters, and removes the only genuine hazard this conversion has. That is a cheaper habit than being right about which abbreviation the recipient uses.

The unit changes when the number stops being about an object and starts being about a quantity. Four hundred boxes weigh 4,270 kg individually and 4.27 t as a consignment; the second figure is what goes on the booking, and the first is what the warehouse handles. Freight, waste, agricultural yield, construction materials and industrial output all cross that line at roughly the same place.

What does not cross it is anything with a limit attached. Vehicle weights stay in kilograms — a gross vehicle weight of 3,500 kg, an axle limit of 11,500 kg — because the limit is a threshold and a threshold written as 3.5 t invites the rounding that a threshold cannot tolerate. Convert for reporting; keep the kilogram figure for compliance.

The conversion loses nothing and the rounding afterwards can lose a great deal. One decimal place of a tonne is 100 kg, two is 10 kg, three is 1 kg — so a total of 4,270 kg quoted as 4.3 t has quietly discarded thirty kilograms, and a total of 12,480 kg quoted as 12.5 t has discarded twenty.

That matters wherever the tonne figure will be multiplied by a price. At a rate per tonne, rounding up gains the seller and rounding down gains the buyer, and neither is an error either party will notice on one line of an invoice. Three decimals is the honest default for a mass that was measured in whole kilograms, because the third decimal place of a tonne is exactly the kilogram the scale reported.

Provenance settles it more often than notation does. International shipping documents, emissions inventories and European industrial figures are metric tonnes; American domestic industry — mining, steel, agriculture, waste — quotes short tons; British sources from before metrication quote long tons. A figure that is round in kilograms started metric, and a figure that is round in pounds did not.

The check that costs nothing is to convert and look for the round number. A quoted "22 tons" that comes out as 19,958 kg was probably 22 short tons and was probably meant to be about twenty tonnes; a quoted "20 tons" that is 20,000 kg exactly is a tonne figure and needs no interpretation. When neither side is round, ask, because the two answers are ten per cent apart and no amount of arithmetic will choose between them.

Aggregate, sand, soil and concrete are sold by mass and consumed by volume, which puts a density between the order and the job. Dry sand or gravel runs around one and a half tonnes to the cubic metre, so a 1,500 kg bulk bag is roughly a cubic metre of it — and the same bag of a wetter or denser material is less.

The kilogram-to-tonne conversion is exact and the volume estimate is not, which is the asymmetry to keep in mind when ordering. The mass figure on the delivery note is a measurement; the cubic metres it fills is a calculation with a variable in it. Order against the mass, plan against the volume, and expect the second to move by ten per cent with the weather.

Greenhouse gas reporting is done in tonnes of carbon dioxide equivalent, and the conventions around it are unusually careful about saying so — "tCO2e" rather than a bare t, because the quantity is a mass of one gas standing in for a mixture of several. Anything below about a tonne is normally kept in kilograms rather than written as a fraction.

Two things make the unit worth checking anyway. Some American domestic figures are published in short tons, which makes a like-for-like comparison with an international inventory about nine per cent out before anything else is considered. And a figure per unit of production — kilograms per item, tonnes per tonne of output — has to have both of its units read, because a ratio with a ton in it can be wrong twice.

A manifest is a list of kilogram figures, and the total should be produced in kilograms and converted once. Converting each line to tonnes and adding the results introduces a rounding per line, and forty lines rounded to two decimals can drift by a couple of hundred kilograms in the direction the roundings happen to lean.

The same applies in reverse to any allocation. Splitting a 4.27 t consignment across three destinations is better done on 4,270 kg, where the remainder is a whole number of kilograms and the parts add back exactly. Keep the small unit for the arithmetic and the large one for the statement — the conversion is free and can be done at either end, so do it at the end where it costs nothing.