Introduction / overview

Torr to atm Conversion turns a pressure reading in torr into standard atmospheres (atm) and back, then goes further with the metric, imperial, and water-column units you're most likely to meet — pascals through gigapascals, psi and lb/ft², and cm or mm of water column.

Type a pressure into any field and every other unit recalculates instantly. Start from torr and read atm, or start from atm and read torr — the conversion works in both directions.

It's the tool for the recurring mismatch where a vacuum pump is rated in torr, a spec sheet quotes atmospheres, and your gauge reads psi or pascals. The Conversion to other units section keeps those extra units in view so you can read the exact value you need without re-entering anything.

How to use / quick start

1Enter the pressure in the field whose unit you already have — Pressure in torrs, Pressure in atmospheres, or any of the units under Conversion to other units.
2Read the equivalent value in the other fields. Because the conversion is two-way, you can type into the atmospheres field first and read torr, or mix units freely.
3Need a unit that isn't shown up front? Open Conversion to other units, pick a unit such as $\mathrm{Pa}$ , $\mathrm{psi}$ , or $\mathrm{cm\,H_2O}$ , and enter the value there.

Example: converting 800 torr to atmospheres

Type $800$ in the Pressure in torrs field. Because one torr is exactly $1/760$ of an atmosphere, the calculator divides by 760:

\frac{800\ \mathrm{Torr}}{760}

=

1.05263\ \mathrm{atm}

The same pressure shows as $106,657.89\ \mathrm{Pa}$ and $15.4694\ \mathrm{psi}$ in the other-unit fields. Going the other way works too: entering $2.5$ in the atmospheres field returns $1,900\ \mathrm{Torr}$ , because $2.5 \times 760 = 1900$ .

Calculation method

The torr is defined as exactly one 760th of a standard atmosphere, so the torr-to-atm step is a single division by 760 — and the reverse is a single multiplication by 760.

P_{\mathrm{atm}} = \frac{P_{\mathrm{Torr}}}{760}

P_{\mathrm{Torr}}

=

760 \times P_{\mathrm{atm}}

To reach any other unit, every pressure is converted through the pascal, the SI derived unit of pressure. A standard atmosphere is exactly $101,325\ \mathrm{Pa}$ , so one torr works out to $101325/760 \approx 133.322\ \mathrm{Pa}$ — the same factor the NIST conversion tables list for torr.

P_{\mathrm{target}}

=

P_{\mathrm{Torr}} \times \frac{101325}{760 \times f_{\mathrm{target}}}

How to read the method:

$f_{\mathrm{target}}$ is the number of pascals in one unit of the target scale, such as $1$ for $\mathrm{Pa}$ , $1000$ for $\mathrm{kPa}$ , $\approx 6894.757$ for $\mathrm{psi}$ , or $98.0665$ for $\mathrm{cm\,H_2O}$ .
Because every editable field is a starting point, the same relationship runs from atm, pascals, psi, or any other unit back to torr — not only from torr outward.
The conversion factors come from exact definitions: the standard atmosphere and the international inch, pound, and standard gravity, all as published by NIST's Guide to the SI, Appendix B.8.

Torr vs. mmHg and other units

Torr and mmHg are almost — but not exactly — the same

Both units grew out of mercury barometers: torr is named after Evangelista Torricelli, and mmHg is the hydrostatic pressure of a one-millimetre mercury column at $0\,^{\circ}\mathrm{C}$ . The conventional mmHg works out to $133.322387415\ \mathrm{Pa}$ , while the torr is $101325/760 \approx 133.32237\ \mathrm{Pa}$ . NIST's own conversion table rounds both to $133.3224\ \mathrm{Pa}$ .

The real difference is about one part in seven million — far too small to matter in vacuum, weather, or lab work. In practice you can treat $1\ \mathrm{Torr}$ and $1\ \mathrm{mmHg}$ as equal, and a mmHg reading can be typed straight into the torr field. If your work needs a dedicated mmHg field with the full list of pressure units, the Pressure Conversion calculator covers mmHg, inHg, bar, and technical atmospheres alongside torr.

A handy anchor: one standard atmosphere

A standard atmosphere is exactly $101,325\ \mathrm{Pa}$ — roughly the average air pressure at sea level — and it gives you a clean set of reference numbers for every field:

1\ \mathrm{atm}

=

760\ \mathrm{Torr}

=

101,325\ \mathrm{Pa}

\approx

14.696\ \mathrm{psi}

Enter $760$ in the torr field and every other unit reads exactly one atmosphere — a useful sanity check that the values in front of you line up.

Which unit fits which job

Torr and mmHg show up on vacuum pumps, vacuum gauges, and low-pressure lab instruments.
Atmospheres appear in meteorology, altitude and diving references, and many engineering tables.
Pascals (and kPa/MPa) are the SI standard used in science and engineering, while psi is common on tires, tools, and U.S. equipment.
cmH₂O and mmH₂O (water column) are used for very low pressures, such as ventilator settings and fluid-head measurements.

Frequently asked questions

Q

Is torr the same as mmHg?

Practically yes. The two differ by about one part in seven million, so a mmHg reading can be entered straight into the torr field with no meaningful error.

Q

Can I convert from atmospheres to torr?

Yes. Type a value into the Pressure in atmospheres field and the torr field updates automatically. For example, $2.5\ \mathrm{atm}$ reads as $1,900\ \mathrm{Torr}$ .

Q

Can a pressure be negative?

Yes. Gauge and vacuum pressures can be negative, so the converter keeps the sign — a value like $-50\ \mathrm{Torr}$ converts to $-0.0657895\ \mathrm{atm}$ instead of being rejected.

Torr to atm Conversion

Introduction / overview

How to use / quick start

Calculation method

Frequently asked questions

Is torr the same as mmHg?

Can I convert from atmospheres to torr?

Can a pressure be negative?

Limitations

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