**Introduction to mmHg**

mmHg is certainly a very important calculation in Physics. Millimetre of mercury is the short form for a millimetre of mercury.

Also, it is a measuring unit that measures the pressure in the manometric unit. Besides, in this topic, we will discuss what is a millimetre of mercury and how to calculate mmHg?

**Millimetre of Mercury**

It is a unit of measure that uses the manometric unit to tell the pressure of the objects. Besides, one can describe it as the extra pressure whose production takes place by a column of mercury one millimetre high. Also, it is currently defined as exactly 133.3223 Pascals.

Moreover, we denote it with mmHg or mm Hg. In this the mm represents millimetre and Hg is the chemical name of mercury or the symbol for mercury.

Furthermore, the millimetre of mercury is still routinely used in medicine, aviation, meteorology, and many other scientific fields. In addition, one millimetre of mercury is approximately 1 Torr which is 1 / 760 of standard atmospheric pressure (101325 / 760 ≈ 133.322368421053 Pascals).

Moreover, these two units are not equal and the relative difference (less than 0.000015 per cent) is minor for most practical use. Also, mercury manometer is the first and most accurate pressure gauge. But, they are no longer in usage due to the toxicity of mercury.

Furthermore, the sensitivity of mercury columns to temperature and local gravity and the better convenience of other instrumentation also reduce their use. In addition, they displayed the pressure alteration among two fluids as a vertical variance between the mercury levels of two connected reservoirs.

**How to calculate mmHg?**

As discussed earlier we know that one millimetre of mercury is the pressure exerted by a 1mm vertical column of mercury at 0 degree Celsius. And we also know that one mmHg is also equal to 1 torr, which is 1 / 760 of atmospheric pressure (atm) that is 1 atm = 760 mmHg.

Moreover, the unit of a millimetre of mercury is considered obsolete and the S.I unit Pascal (Pa; 1 atm = 1,01,325 Pa) ought to be used. In addition, the mmHg is still widely used in the B.P. machines (Blood Pressure Machines).

**Using the basic definition of mmHg calculate the blood pressure of 120 mm****Hg.**

Pressure = Hg Density × Standard Gravity × Mercury Height

Mercury (Hg) density is 13.5951 g/cm^{3} (133595.1 kg/m^{3}), and the standard gravity is 9.80665 m/s^{2}. Also, note that 120 mm is 0.12 m.

Pressure = 13595.1 kg/m^{3} × 9.80665 m/s^{2} × 0.12 m = 15998.69 Pa

Now we obtain the relation between 1 Pa and 1 mmHg. Let’s consider 1 atm = 1,01,325 Pa, and 1 atm = 760 mmHg (As discussed earlier). So, we can conclude that 1,01,325 Pa = 760 mmHg. Now multiply both side of the equation by 1 / 760 you would get:

1 mmHg = 1 Pa × 1,01,325 / 760

**Now to covert pressure Pa using proportion the Formula is:**

Suppose 1 mmHg resembles to 1 Pa × 1,01,325 / 760 pressure (mm Hg) resembles to pressure (Pa).

The solution of this problem produces the formula:

Pressure (mm Hg) = Pressure (Pa) × 760 / 1,01,325 = pressure (Pa) × 0.0075

**Now calculate the pressure of 36,000 Pa using this same formula from step three:**

Pressure = 36,000 Pa × 0.0075 = 270.02 mmHg

**Solved Question for You**

**Question.** What is the pressure of mm Hg if Pa is 48000?

**A.** 350.02956

**B.** 340.02956

**C.** 370.02956

**D.** 360.02956

**Answer.** The correct answer is option D.

Pressure = 48,000 Pa × 0.0075 = 360.02956