The Pascal, named after the French mathematician and physicist Blaise Pascal, is the SI unit of pressure. It is equivalent to one newton per square meter, symbolized as Pa. Despite its relatively recent introduction in 1971, the Pascal honors the pioneering work of Pascal in fluid mechanics and pressure, such as Pascal’s Law, which explains how pressure applied to a confined fluid is transmitted undiminished in all directions. Interestingly, a single Pascal is a tiny unit of pressure, roughly equal to the pressure exerted by a dollar bill resting flat on a table. This illustrates why everyday atmospheric pressure is typically measured in kilopascals (kPa), as one standard atmosphere is about 101.3 kPa.
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.
Pascals | Millimeters of mercury |
---|---|
0
Pa
|
0
mmHg
|
1000
Pa
|
7.50064
mmHg
|
2000
Pa
|
15.00128
mmHg
|
3000
Pa
|
22.50191
mmHg
|
4000
Pa
|
30.00255
mmHg
|
5000
Pa
|
37.50319
mmHg
|
6000
Pa
|
45.00383
mmHg
|
7000
Pa
|
52.50446
mmHg
|
8000
Pa
|
60.0051
mmHg
|
9000
Pa
|
67.50574
mmHg
|
10000
Pa
|
75.00638
mmHg
|
11000
Pa
|
82.50701
mmHg
|
12000
Pa
|
90.00765
mmHg
|
13000
Pa
|
97.50829
mmHg
|
14000
Pa
|
105.00893
mmHg
|
15000
Pa
|
112.50956
mmHg
|
16000
Pa
|
120.0102
mmHg
|
17000
Pa
|
127.51084
mmHg
|
18000
Pa
|
135.01148
mmHg
|
19000
Pa
|
142.51211
mmHg
|
20000
Pa
|
150.01275
mmHg
|
21000
Pa
|
157.51339
mmHg
|
22000
Pa
|
165.01403
mmHg
|
23000
Pa
|
172.51466
mmHg
|
24000
Pa
|
180.0153
mmHg
|
25000
Pa
|
187.51594
mmHg
|
26000
Pa
|
195.01658
mmHg
|
27000
Pa
|
202.51721
mmHg
|
28000
Pa
|
210.01785
mmHg
|
29000
Pa
|
217.51849
mmHg
|
30000
Pa
|
225.01913
mmHg
|
31000
Pa
|
232.51976
mmHg
|
32000
Pa
|
240.0204
mmHg
|
33000
Pa
|
247.52104
mmHg
|
34000
Pa
|
255.02168
mmHg
|
35000
Pa
|
262.52231
mmHg
|
36000
Pa
|
270.02295
mmHg
|
37000
Pa
|
277.52359
mmHg
|
38000
Pa
|
285.02423
mmHg
|
39000
Pa
|
292.52486
mmHg
|
40000
Pa
|
300.0255
mmHg
|
41000
Pa
|
307.52614
mmHg
|
42000
Pa
|
315.02678
mmHg
|
43000
Pa
|
322.52741
mmHg
|
44000
Pa
|
330.02805
mmHg
|
45000
Pa
|
337.52869
mmHg
|
46000
Pa
|
345.02933
mmHg
|
47000
Pa
|
352.52997
mmHg
|
48000
Pa
|
360.0306
mmHg
|
49000
Pa
|
367.53124
mmHg
|
50000
Pa
|
375.03188
mmHg
|
51000
Pa
|
382.53252
mmHg
|
52000
Pa
|
390.03315
mmHg
|
53000
Pa
|
397.53379
mmHg
|
54000
Pa
|
405.03443
mmHg
|
55000
Pa
|
412.53507
mmHg
|
56000
Pa
|
420.0357
mmHg
|
57000
Pa
|
427.53634
mmHg
|
58000
Pa
|
435.03698
mmHg
|
59000
Pa
|
442.53762
mmHg
|
60000
Pa
|
450.03825
mmHg
|
61000
Pa
|
457.53889
mmHg
|
62000
Pa
|
465.03953
mmHg
|
63000
Pa
|
472.54017
mmHg
|
64000
Pa
|
480.0408
mmHg
|
65000
Pa
|
487.54144
mmHg
|
66000
Pa
|
495.04208
mmHg
|
67000
Pa
|
502.54272
mmHg
|
68000
Pa
|
510.04335
mmHg
|
69000
Pa
|
517.54399
mmHg
|
70000
Pa
|
525.04463
mmHg
|
71000
Pa
|
532.54527
mmHg
|
72000
Pa
|
540.0459
mmHg
|
73000
Pa
|
547.54654
mmHg
|
74000
Pa
|
555.04718
mmHg
|
75000
Pa
|
562.54782
mmHg
|
76000
Pa
|
570.04845
mmHg
|
77000
Pa
|
577.54909
mmHg
|
78000
Pa
|
585.04973
mmHg
|
79000
Pa
|
592.55037
mmHg
|
80000
Pa
|
600.051
mmHg
|
81000
Pa
|
607.55164
mmHg
|
82000
Pa
|
615.05228
mmHg
|
83000
Pa
|
622.55292
mmHg
|
84000
Pa
|
630.05355
mmHg
|
85000
Pa
|
637.55419
mmHg
|
86000
Pa
|
645.05483
mmHg
|
87000
Pa
|
652.55547
mmHg
|
88000
Pa
|
660.0561
mmHg
|
89000
Pa
|
667.55674
mmHg
|
90000
Pa
|
675.05738
mmHg
|
91000
Pa
|
682.55802
mmHg
|
92000
Pa
|
690.05865
mmHg
|
93000
Pa
|
697.55929
mmHg
|
94000
Pa
|
705.05993
mmHg
|
95000
Pa
|
712.56057
mmHg
|
96000
Pa
|
720.06121
mmHg
|
97000
Pa
|
727.56184
mmHg
|
98000
Pa
|
735.06248
mmHg
|
99000
Pa
|
742.56312
mmHg
|
100000
Pa
|
750.06376
mmHg
|
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