The millimeter of mercury (mmHg) is a unit of pressure traditionally used in medicine and meteorology, and its history dates back to the barometer invention by Evangelista Torricelli in 1643. Often, it is associated with measuring blood pressure and intraocular pressure, representing the pressure exerted by a column of mercury precisely 1 millimeter high. This fascinating unit highlights the interplay of physics and medicine, reflecting both the force of blood circulating against vessel walls and the atmospheric pressure’s effects on our weather systems.

Interestingly, mmHg is one of the few units still officially sanctioned for use with SI (International System of Units) under specific legal and medical contexts, underscoring its importance over centuries. Despite the global shift towards using Pascals for pressure, mmHg remains ingrained in clinical settings because of its historical usage and direct relation to human physiology. Its origins and continued use illustrate how historical scientific instruments still influence modern practices.

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The “inch of mercury” (inHg) is a unit of pressure commonly used in aviation, meteorology, and refrigeration. It originates from the barometric pressure measurement practice using a column of mercury. This unit became a staple due to its early adoption in weather forecasting and its accurate and consistent measurements. An interesting fact is that an inch of mercury is approximately equal to 33.86 millibars or 3386 Pascals, but what truly distinguishes it is its historical significance in the development of modern atmospheric science.

In the 17th century, Evangelista Torricelli, a student of Galileo, first discovered that atmospheric pressure could sustain a column of mercury, laying the groundwork for this unit. His invention, the barometer, revolutionized how we understand and predict weather, marking the inch of mercury as more than just a unit—it’s a nod to the evolution of scientific inquiry and practice.

Millimeters of mercury

Inches of mercury

0 mmHg

0 inHg

10 mmHg

0.3937 inHg

20 mmHg

0.787399 inHg

30 mmHg

1.1811 inHg

40 mmHg

1.5748 inHg

50 mmHg

1.9685 inHg

60 mmHg

2.3622 inHg

70 mmHg

2.7559 inHg

80 mmHg

3.1496 inHg

90 mmHg

3.5433 inHg

100 mmHg

3.937 inHg

110 mmHg

4.3307 inHg

120 mmHg

4.7244 inHg

130 mmHg

5.11809 inHg

140 mmHg

5.51179 inHg

150 mmHg

5.90549 inHg

160 mmHg

6.29919 inHg

170 mmHg

6.69289 inHg

180 mmHg

7.08659 inHg

190 mmHg

7.48029 inHg

200 mmHg

7.87399 inHg

210 mmHg

8.26769 inHg

220 mmHg

8.66139 inHg

230 mmHg

9.05509 inHg

240 mmHg

9.44879 inHg

250 mmHg

9.84249 inHg

260 mmHg

10.23619 inHg

270 mmHg

10.62989 inHg

280 mmHg

11.02359 inHg

290 mmHg

11.41729 inHg

300 mmHg

11.81099 inHg

310 mmHg

12.20469 inHg

320 mmHg

12.59839 inHg

330 mmHg

12.99209 inHg

340 mmHg

13.38579 inHg

350 mmHg

13.77949 inHg

360 mmHg

14.17319 inHg

370 mmHg

14.56689 inHg

380 mmHg

14.96059 inHg

390 mmHg

15.35428 inHg

400 mmHg

15.74798 inHg

410 mmHg

16.14168 inHg

420 mmHg

16.53538 inHg

430 mmHg

16.92908 inHg

440 mmHg

17.32278 inHg

450 mmHg

17.71648 inHg

460 mmHg

18.11018 inHg

470 mmHg

18.50388 inHg

480 mmHg

18.89758 inHg

490 mmHg

19.29128 inHg

500 mmHg

19.68498 inHg

510 mmHg

20.07868 inHg

520 mmHg

20.47238 inHg

530 mmHg

20.86608 inHg

540 mmHg

21.25978 inHg

550 mmHg

21.65348 inHg

560 mmHg

22.04718 inHg

570 mmHg

22.44088 inHg

580 mmHg

22.83458 inHg

590 mmHg

23.22828 inHg

600 mmHg

23.62198 inHg

610 mmHg

24.01568 inHg

620 mmHg

24.40938 inHg

630 mmHg

24.80308 inHg

640 mmHg

25.19677 inHg

650 mmHg

25.59047 inHg

660 mmHg

25.98417 inHg

670 mmHg

26.37787 inHg

680 mmHg

26.77157 inHg

690 mmHg

27.16527 inHg

700 mmHg

27.55897 inHg

710 mmHg

27.95267 inHg

720 mmHg

28.34637 inHg

730 mmHg

28.74007 inHg

740 mmHg

29.13377 inHg

750 mmHg

29.52747 inHg

760 mmHg

29.92117 inHg

770 mmHg

30.31487 inHg

780 mmHg

30.70857 inHg

790 mmHg

31.10227 inHg

800 mmHg

31.49597 inHg

810 mmHg

31.88967 inHg

820 mmHg

32.28337 inHg

830 mmHg

32.67707 inHg

840 mmHg

33.07077 inHg

850 mmHg

33.46447 inHg

860 mmHg

33.85817 inHg

870 mmHg

34.25187 inHg

880 mmHg

34.64557 inHg

890 mmHg

35.03927 inHg

900 mmHg

35.43296 inHg

910 mmHg

35.82666 inHg

920 mmHg

36.22036 inHg

930 mmHg

36.61406 inHg

940 mmHg

37.00776 inHg

950 mmHg

37.40146 inHg

960 mmHg

37.79516 inHg

970 mmHg

38.18886 inHg

980 mmHg

38.58256 inHg

990 mmHg

38.97626 inHg

1000 mmHg

39.36996 inHg

Conversion

Millimeters of mercury to Pascals

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Millimeters of mercury to Kilopascals

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Millimeters of mercury to Megapascals

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Millimeters of mercury to Hectopascals

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Millimeters of mercury to Millibar

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Millimeters of mercury to Bar

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Millimeters of mercury to Torr

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Millimeters of mercury to Meters of water @ 4°C

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Millimeters of mercury to Pounds per square inch

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Millimeters of mercury to Kilopound per square inch

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Millimeters of mercury to Inches of mercury Conversion

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> Millimeters of mercury to Inches of mercury Conversion Table

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:: Pressure Units

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