Torr to atmospheres

One torr is 0.001315789474 atmospheres, 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 torr is 0.001315789474 atmospheres. 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 torr is exactly one 760th of an atmosphere.

The atmosphere is defined as exactly 101,325 pascals. Not quite a bar.

The number in your head

Most people use 0.0013 for this, which is the factor to two significant figures. It is low by 1.2% — 12 atmospheres too few in every thousand, and 120 in every ten thousand.

Going the other way

The reverse is not this sum backwards in your head. It is a different factor, 760, 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 torr, your figure is already uncertain by half of one — so the answer is uncertain by about 0.000658 atmospheres, and every digit past that is decoration. Quoting 0.00162442 when you measured with a tape is claiming a precision the tape never had.

Where these two sit

Torr and atmospheres both measure pressure, 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 torr with mmHg rather than with atmospheres, because that is the conversion people ask for most. This page exists because a good many ask for this one instead.