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 “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.
Pascals | Inches of mercury |
---|---|
0
Pa
|
0
inHg
|
1000
Pa
|
0.2953
inHg
|
2000
Pa
|
0.5906
inHg
|
3000
Pa
|
0.885899
inHg
|
4000
Pa
|
1.1812
inHg
|
5000
Pa
|
1.4765
inHg
|
6000
Pa
|
1.7718
inHg
|
7000
Pa
|
2.0671
inHg
|
8000
Pa
|
2.3624
inHg
|
9000
Pa
|
2.6577
inHg
|
10000
Pa
|
2.953
inHg
|
11000
Pa
|
3.2483
inHg
|
12000
Pa
|
3.5436
inHg
|
13000
Pa
|
3.8389
inHg
|
14000
Pa
|
4.1342
inHg
|
15000
Pa
|
4.4295
inHg
|
16000
Pa
|
4.7248
inHg
|
17000
Pa
|
5.0201
inHg
|
18000
Pa
|
5.3154
inHg
|
19000
Pa
|
5.6107
inHg
|
20000
Pa
|
5.906
inHg
|
21000
Pa
|
6.2013
inHg
|
22000
Pa
|
6.4966
inHg
|
23000
Pa
|
6.7919
inHg
|
24000
Pa
|
7.0872
inHg
|
25000
Pa
|
7.3825
inHg
|
26000
Pa
|
7.67779
inHg
|
27000
Pa
|
7.97309
inHg
|
28000
Pa
|
8.26839
inHg
|
29000
Pa
|
8.56369
inHg
|
30000
Pa
|
8.85899
inHg
|
31000
Pa
|
9.15429
inHg
|
32000
Pa
|
9.44959
inHg
|
33000
Pa
|
9.74489
inHg
|
34000
Pa
|
10.04019
inHg
|
35000
Pa
|
10.33549
inHg
|
36000
Pa
|
10.63079
inHg
|
37000
Pa
|
10.92609
inHg
|
38000
Pa
|
11.22139
inHg
|
39000
Pa
|
11.51669
inHg
|
40000
Pa
|
11.81199
inHg
|
41000
Pa
|
12.10729
inHg
|
42000
Pa
|
12.40259
inHg
|
43000
Pa
|
12.69789
inHg
|
44000
Pa
|
12.99319
inHg
|
45000
Pa
|
13.28849
inHg
|
46000
Pa
|
13.58379
inHg
|
47000
Pa
|
13.87909
inHg
|
48000
Pa
|
14.17439
inHg
|
49000
Pa
|
14.46969
inHg
|
50000
Pa
|
14.76499
inHg
|
51000
Pa
|
15.06029
inHg
|
52000
Pa
|
15.35559
inHg
|
53000
Pa
|
15.65089
inHg
|
54000
Pa
|
15.94619
inHg
|
55000
Pa
|
16.24149
inHg
|
56000
Pa
|
16.53679
inHg
|
57000
Pa
|
16.83209
inHg
|
58000
Pa
|
17.12739
inHg
|
59000
Pa
|
17.42269
inHg
|
60000
Pa
|
17.71799
inHg
|
61000
Pa
|
18.01329
inHg
|
62000
Pa
|
18.30859
inHg
|
63000
Pa
|
18.60389
inHg
|
64000
Pa
|
18.89919
inHg
|
65000
Pa
|
19.19449
inHg
|
66000
Pa
|
19.48979
inHg
|
67000
Pa
|
19.78509
inHg
|
68000
Pa
|
20.08039
inHg
|
69000
Pa
|
20.37569
inHg
|
70000
Pa
|
20.67099
inHg
|
71000
Pa
|
20.96629
inHg
|
72000
Pa
|
21.26159
inHg
|
73000
Pa
|
21.55689
inHg
|
74000
Pa
|
21.85219
inHg
|
75000
Pa
|
22.14749
inHg
|
76000
Pa
|
22.44279
inHg
|
77000
Pa
|
22.73809
inHg
|
78000
Pa
|
23.03338
inHg
|
79000
Pa
|
23.32868
inHg
|
80000
Pa
|
23.62398
inHg
|
81000
Pa
|
23.91928
inHg
|
82000
Pa
|
24.21458
inHg
|
83000
Pa
|
24.50988
inHg
|
84000
Pa
|
24.80518
inHg
|
85000
Pa
|
25.10048
inHg
|
86000
Pa
|
25.39578
inHg
|
87000
Pa
|
25.69108
inHg
|
88000
Pa
|
25.98638
inHg
|
89000
Pa
|
26.28168
inHg
|
90000
Pa
|
26.57698
inHg
|
91000
Pa
|
26.87228
inHg
|
92000
Pa
|
27.16758
inHg
|
93000
Pa
|
27.46288
inHg
|
94000
Pa
|
27.75818
inHg
|
95000
Pa
|
28.05348
inHg
|
96000
Pa
|
28.34878
inHg
|
97000
Pa
|
28.64408
inHg
|
98000
Pa
|
28.93938
inHg
|
99000
Pa
|
29.23468
inHg
|
100000
Pa
|
29.52998
inHg
|
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