Torr to Atmospheres Converter
760 Torr = 1 atm exactly. Type in either box.
—
Seven hundred and sixty to one
The torr is defined as exactly one seven-hundred-and-sixtieth of a standard atmosphere. That awkward-looking number has a reason: a mercury barometer at sea level stands about 760 mm high, and the torr was built to make one millimetre of mercury equal one torr.
760 Torr = 1 atm exactly
The unit is named after Evangelista Torricelli, who built the first barometer in 1643 and worked out that the column was being held up by the weight of the air.
Torr and mmHg are not formally identical but differ by roughly one part in seven million, which is why blood pressure in mmHg and vacuum pressure in torr are treated as the same unit outside metrology.
The torr
One torr is one seven-hundred-and-sixtieth of an atmosphere, which makes it almost exactly the pressure of one millimetre of mercury. It is named after Torricelli, who built the first barometer in 1643.
It survives in vacuum technology and in medicine, where blood pressure is still reported in millimetres of mercury. The two units differ by about one part in seven million, so outside metrology they are treated as the same.
The standard atmosphere
One atmosphere is defined as exactly 101,325 pascals. It was originally meant to represent average air pressure at sea level, and it is close, but it is now a fixed definition rather than a measurement — real sea-level pressure wanders either side of it with the weather.
The unit is used where pressure is being compared to ordinary air: chemistry, diving, aviation and physiology. Ten metres of seawater adds roughly one atmosphere, which is the rule every diver learns first.
The working, step by step
Every line updates with whatever you type above. The point is the method, which is the same for any pair of units in this family.
The same quantity, two different numbers
One physical amount, read off two scales. The tick marks do not line up, and the gap between them is the conversion factor made visible.
How much is that?
A number is easier to judge next to something familiar.
Your turn
Reading a method and being able to use it are different things. Answer within half a per cent and it counts as correct.
Score: 0 of 0
How to use this converter
- Type into either box. The other side updates as you go; there is no button to press.
- Swap the direction with the button between the boxes, carrying your value across.
- Set the decimals if the default is more or less precision than you need.
- Copy the answer with its unit, ready to paste.
- Use the shortcut buttons for the values that come up most often.
- Share the result. The address bar tracks what you type, so the link you copy opens on the same number.
Common uses and tips
Where pressure conversions come up
- Tyres. The single most common reason anyone converts pressure. American placards are in psi, European and Asian ones in bar or kPa, and the three appear side by side on the same door sticker.
- Weather. Forecasts use hectopascals or millibars, which are the same size — 1 hPa is 1 mbar. A typical high-pressure system reads about 1020 of either.
- Diving. Cylinder pressures are in bar almost everywhere and psi in the United States. A full 200 bar cylinder is about 2,900 psi.
- Coffee. Espresso machines are specified in bar; nine bar at the group head is the usual target, which is about 130 psi.
- Materials and hydraulics. Tensile strength and hydraulic ratings come in MPa or psi, and the two communities rarely use the same one.
The trap: gauge pressure and absolute pressure
Almost every pressure you read off a dial in daily life is gauge pressure — how much higher than the surrounding air it is. A tyre at 32 psi contains 32 psi more than the atmosphere, so its absolute pressure is about 46.7 psi.
Conversion between units never changes which of the two you have. If you start with a gauge reading you end with a gauge reading. Where it goes wrong is in physics and chemistry, where the gas laws need absolute pressure: add one atmosphere to a gauge figure before it goes into a calculation. The units psig and psia exist precisely to keep the two apart.
Tips worth knowing
- One bar is not one atmosphere. It is 0.9869 of one. The difference is small enough to ignore for a tyre and large enough to matter in a laboratory.
- Millibars and hectopascals are identical. Weather maps use whichever the local service prefers; the number is the same.
- One MPa is about ten atmospheres, which makes megapascals easy to sanity-check against everyday pressures.
- Torr and mmHg are interchangeable in practice, differing by about one part in seven million.
Values people look up most
Each one opens the converter with the number already in it.
- 1 Torr to atm
- 10 Torr to atm
- 50 Torr to atm
- 100 Torr to atm
- 200 Torr to atm
- 300 Torr to atm
- 380 Torr to atm
- 400 Torr to atm
- 500 Torr to atm
- 600 Torr to atm
- 700 Torr to atm
- 760 Torr to atm
- 800 Torr to atm
- 1,000 Torr to atm
- 1,520 Torr to atm
- 3,800 Torr to atm
Quick reference
| Torr | Atmospheres |
|---|---|
| 1 Torr | 0.001316 atm |
| 10 Torr | 0.013158 atm |
| 100 Torr | 0.131579 atm |
| 200 Torr | 0.263158 atm |
| 380 Torr | 0.5 atm |
| 500 Torr | 0.657895 atm |
| 760 Torr | 1 atm |
| 1,000 Torr | 1.315789 atm |
| 1,520 Torr | 2 atm |
| 3,800 Torr | 5 atm |
| 7,600 Torr | 10 atm |
Questions people ask
How many torr in an atmosphere?
Exactly 760, by definition.
Is torr the same as mmHg?
Very nearly. They differ by about one part in seven million, which matters only in metrology.
Where is torr still used?
Vacuum technology and medicine. Blood pressure readings such as 120/80 are in millimetres of mercury.
Does this convert gauge or absolute pressure?
Whichever you put in. Converting units does not change which kind of pressure you have — a gauge reading converts to a gauge reading. If a calculation needs absolute pressure, add one atmosphere first.