Convert Pressure from torr to millimeters of mercury (torr to mmHg)

Torr to Millimeter of Mercury Conversion Formula

For every practical purpose, torr and millimeters of mercury are the same unit:

• mmHg ≈ torr × 1

The torr was created as a tribute to Evangelista Torricelli, inventor of the mercury barometer, and was originally defined as one millimeter of mercury. Modern metrology split the definitions — the torr is now exactly 1/760 of a standard atmosphere (101,325/760 Pa), while the conventional mmHg is defined through mercury's density as 133.322 Pa — and the two definitions land a hair's breadth apart. This calculator, following its conversion library's rounded constants, reports 1 torr = 1.0000028 mmHg; the physically exact discrepancy is even smaller, about two parts in ten million. No instrument on earth resolves the difference.

Step-by-Step Example

A vacuum gauge reads 250 torr and a legacy process sheet wants mmHg:

1. Take the pressure: 250 torr
2. Multiply by 1: 250 mmHg

Done. At six significant figures the calculator shows 250.001 mmHg — a difference with no physical meaning at any realistic precision.

Quick Reference Table

One Unit, Two Communities

The practical question is never "how do I convert" but "why do both names exist". Vacuum science and semiconductor processing say torr — chamber base pressures of 10⁻⁶ torr, sputtering recipes at millitorr — while medicine and physiology say mmHg — blood pressure of 120/80, blood-gas tensions, intracranial and intraocular pressures. Same unit, different heritage, and documents almost never mix them; converting between them is really an act of translation between fields. The trap worth flagging sits nearby: neither torr nor mmHg is a millibar. A millibar is 0.750 mmHg, and vacuum equipment sold across the Atlantic often carries one gauge scale in torr and another in mbar — reading the wrong scale introduces a 33% error, which has ruined more than one process run. When a figure's provenance is unclear, anchor on the atmosphere: 760 torr = 760 mmHg = 1,013.25 mbar.

How many torr are in one millimeter of mercury? One millimeter of mercury (mmHg) contains 0.99999723661485319516 torr (torr) — the inverse of the factor above. Multiplying by 1.0000027633927831234 takes you from torr to millimeters of mercury; multiplying by 0.99999723661485319516 brings you back.

Put in words: one torr equals 1.0000027633927831234 millimeters of mercury, so the torr is the larger unit of this pair. Converting between them never changes the amount of pressure being measured — only the size of the unit you count it in.

What Is a Torr?

A torr (Torr) is a unit of pressure.

It is primarily used to measure a vacuum, or pressures much lower than the air pressure we experience every day.

While the modern standard (SI) unit for pressure is the pascal (Pa), the torr is still widely used in many scientific and engineering fields.

For conversion, one torr is equal to about 133.32 pascals.

A much simpler way to think about it is in relation to our atmosphere: one standard atmosphere (atm) is defined as exactly 760 Torr.

Where Did the Torr Come From?

The unit is named in honor of Evangelista Torricelli, the 17th-century Italian physicist who invented the mercury barometer.

Because of this, one torr was initially defined as being equal to one millimeter of mercury (mmHg).

This means 1 Torr is the pressure exerted by a column of mercury that is one millimeter high.

Torr vs. Atmosphere (atm)

As mentioned, the torr's most convenient relationship is with the standard atmosphere (atm).

One standard atmosphere—the average air pressure at sea level—is set at exactly 760 Torr.

This straightforward, whole-number conversion makes the torr a popular choice for anyone working with fractions of atmospheric pressure.

Where Is the Torr Used Today?

The torr is the primary unit of measurement for high-vacuum and ultra-high-vacuum technology.

Because it is such a small unit (it takes 760 of them to equal one atmosphere), it is ideal for quantifying pressures far below normal air pressure.

You will find the torr used in many advanced scientific and industrial fields, including:

• Semiconductor manufacturing
• Thin-film deposition (like adding anti-reflective coatings to glasses)
• Mass spectrometry
• Particle accelerators
• Vacuum furnaces

What Is a Millimeter of Mercury (mmHg)?

A millimeter of mercury (mmHg) is a manometric unit of pressure.

It was historically defined as the pressure generated by a column of mercury exactly one millimeter high.

Today, it is most famous as the unit used in medicine for measuring blood pressure. It is also commonly used in meteorology, aviation, and physics to measure atmospheric pressure or vacuum pressure.

The Origin of the mmHg Unit

The mmHg unit originates from the invention of the barometer by Evangelista Torricelli in 1643.

Torricelli's device measured atmospheric pressure by seeing how high it could support a column of mercury in a tube.

Standard atmospheric pressure was found to support a column approximately 760 mm high, which established 760 mmHg as a standard reference point.

Common Applications of mmHg

The most well-known application of mmHg is in medicine.

• Blood Pressure: Readings are given as two numbers: systolic pressure (when the heart beats) over diastolic pressure (when the heart rests), such as 120/80 mmHg. This is a critical vital sign for human health.

• Meteorology: Used for reporting barometric (atmospheric) pressure, which helps in weather forecasting.

• Physics & Engineering: Used for measuring vacuum pressures and other low-pressure systems where precision is needed.

How to Convert mmHg to Other Pressure Units

While mmHg is common, other pressure units are standard in different fields. Here are the most common conversions:

• 1 mmHg = 133.322 pascals (Pa)
• 1 mmHg = 0.133322 kilopascals (kPa)
• 760 mmHg = 1 standard atmosphere (atm)

torr to millimeter of mercury Conversion Table

Here are some quick reference conversions from torr (torr) to millimeter of mercury (mmHg):

This conversion in other languages

Engineering datasheets across Europe write torr to millimeter of mercury several different ways. The calculation is the same in every one of them.