Convert t to kg

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".

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.

Going from tonnes to kilograms moves the decimal point 3 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 1234000 kg — 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 tonne is not one of the SI units. It sits on the short list of non-SI units accepted for use with SI, alongside the litre, the hour and the degree — units too embedded in ordinary work to legislate away. Its SI equivalent exists and is the megagram, symbol Mg, which appears in some standards documents and essentially nowhere else.

The reason the megagram lost is the kilogram's prefix. A thousand kilograms should be a megagram, but a reader who sees Mg has to work out whether the prefix applies to the gram or the kilogram, and gets a factor of a thousand wrong if they guess. The tonne sidesteps the question by being a separate word, which is exactly what makes it useful and exactly why it is not SI.

Lifting equipment carries a safe working load in kilograms. Pallet racking is rated per beam pair in kilograms. Passenger and goods lifts state a capacity in kilograms and a number of persons. Floor loadings are given in kilonewtons per square metre, which is a kilogram figure once through gravity. None of them is written in tonnes.

Meanwhile the thing being lifted is described in tonnes, because that is how machines, vehicles and bulk materials are sold. So the conversion is the join between two documents that were never written for each other, and the safe habit is to convert the load into the rating's units rather than the rating into the load's — the rating is the number with a legal consequence attached, and it should not be the one that gets rounded.

A weight in tonnes rarely says what it includes. A 24 t container weight might be the payload, the payload plus the container, or the container alone; a machine listed at 3.5 t may or may not include the attachments, the fuel and the ballast. The three words that resolve it are gross, net and tare, and a figure with none of them attached is not yet usable against a limit.

Convert and label in the same step. Writing "3,500 kg gross, including 180 kg of fuel" makes the figure checkable by somebody who was not there; writing "3,500 kg" makes it a number that will be compared against whichever limit is nearest. Where the source document does not say, the difference between the readings is usually recoverable from a weighbridge ticket, and it is worth recovering before the load is planned.

One hundredth of a tonne is ten kilograms and one thousandth is one kilogram. That makes a figure like 7.5 t a statement accurate to about a hundred kilograms unless something says otherwise — which is fine for a vehicle and useless for a batch of material where the difference between 7,450 and 7,550 kg is a rejected delivery.

The rule of thumb is that a tonne figure carries as many kilograms of uncertainty as the last digit implies, and that is often much larger than the instrument's. A weighbridge reads to 20 kg; quoting its output as 24.5 t discards resolution that was already paid for. Where the number is going into a total, keep the kilograms and convert the total once.

Prices, yields and emission factors are almost all written per tonne: so many euros a tonne for steel, so many tonnes a hectare for a crop, so many kilograms of CO2 a tonne for a material. The quantity on the invoice is a tonne figure and the quantity on the loading dock is a kilogram figure, and the two have to be reconciled at the point where the material is actually weighed.

That reconciliation is where the conversion earns its place. A 0.5 % moisture allowance on a 22 t delivery is 110 kg, which is a number a driver and a receiving clerk can both check on a scale, while 0.11 t is a number nobody weighs. Converting to kilograms is not a formality here; it puts the disputed quantity in the unit the dispute will be settled in.

Since 2016 a packed shipping container cannot be loaded onto a vessel without a verified gross mass declared by the shipper, and that declaration is made in kilograms. The container itself is described in tonnes in every commercial conversation about it, so the conversion sits directly on a document with a legal consequence and a vessel waiting behind it.

The rule exists because guessed weights capsized ships and collapsed stacks. What it means in practice is that the figure has to come from a weighing rather than from a calculation — either the packed container on a weighbridge, or every item plus the tare weight of the box, summed. A tonne figure converted to kilograms is a valid way to express the answer and never a valid way to obtain it.

Road weighbridges commonly read in 20 kg increments, which is 0.02 t. That sets a floor under the precision of any tonne figure that came off one: 24.5 t is a real measurement and 24.517 t is not, and the extra digits appear only because somebody converted from a different unit and printed everything the arithmetic produced.

Knowing the instrument's step also tells you when a discrepancy is worth chasing. Two weighings of the same load 40 kg apart are within two increments and probably the same load; two weighings 400 kg apart are not, and the difference is fuel, a wet tarpaulin, or a load that changed between them. Converting to kilograms is what makes that comparison legible — in tonnes both differences look like rounding.

Mass and space are separate constraints, and a tonne figure says nothing about the second. Dry sand is around 1.6 t per cubic metre, so a tonne of it is roughly 0.6 m³ and will sit in a corner of a small trailer. Baled straw is a fraction of that density, and a tonne of it fills a lorry while leaving most of the payload unused.

That is why haulage is planned against two limits at once: the vehicle's gross weight in tonnes and its usable volume in cubic metres. Converting the mass to kilograms helps with the first and is irrelevant to the second, and a load that is legal on one and impossible on the other is a common and expensive discovery. Where a material is unfamiliar, its bulk density is a more useful number than its weight.