Grams to tonnes
One gram is 0.000001 tonnes, and this shows the working rather than just the answer. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
The factor
One gram is 0.000001 tonnes. That is the whole of the conversion: multiply by it, and nothing else happens.
And it is exact
Not rounded, not measured, not a convention that might be revised. The factor above is the definition, so an answer from it is as exact as the number you typed.
The tonne is 1,000 kg exactly. Also called a metric ton, and not the same as either other ton.
There is no shorter version
The factor is short enough to use as it stands, so nobody carries a rounded one and there is nothing to get wrong.
Going the other way
The reverse is not this sum backwards in your head. It is a different factor, 1,000,000, and dividing by one is not the same as multiplying by a rounded version of the other.
That one is short enough to write down exactly, which is why the conversion feels easier in this direction than the other.
How many of those decimals mean anything
The box above will give you ten decimal places because it can. Whether they mean anything is decided by your measurement, not by the arithmetic.
If you measured to the nearest gram, your figure is already uncertain by half of one — so the answer is uncertain by about 0 tonnes, and every digit past that is decoration. Quoting 0.00000123 when you measured with a tape is claiming a precision the tape never had.
Where these two sit
Grams and tonnes both measure mass, which is why they can be converted at all. A conversion between families — a length into a weight — is not a conversion, it is a question with a missing quantity in it.
The unit converter pairs grams with ounces rather than with tonnes, because that is the conversion people ask for most. This page exists because a good many ask for this one instead.
Other conversions from grams
ounces · kilograms · pounds · milligrams · micrograms · stone