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.
The kilopound per square inch (ksi) is a unit of pressure that is not as commonly encountered as its smaller counterpart, pounds per square inch (psi). However, it plays a crucial role in engineering and materials science, particularly in the United States, where it is often used to express the tensile strength and yield strength of materials like steel. One ksi is equal to 1,000 psi, making it a convenient way to express large values of pressure or stress without cumbersome zeros.
Interestingly, ksi is commonly used in the context of measuring the mechanical properties of metals, especially in aerospace and automotive industries. These are fields where precise and robust materials are essential for safety and performance. For instance, typical structural steel can have a yield strength on the order of 50 ksi, underscoring the immense stress materials can withstand in such applications. Understanding these units helps engineers ensure that the materials used can handle the demanding conditions they face.
Inches of mercury | Kilopound per square inch |
---|---|
0
inHg
|
0
ksi
|
1
inHg
|
0.000491154
ksi
|
2
inHg
|
0.000982308
ksi
|
3
inHg
|
0.00147346
ksi
|
4
inHg
|
0.00196462
ksi
|
5
inHg
|
0.00245577
ksi
|
6
inHg
|
0.00294692
ksi
|
7
inHg
|
0.00343808
ksi
|
8
inHg
|
0.00392923
ksi
|
9
inHg
|
0.00442039
ksi
|
10
inHg
|
0.00491154
ksi
|
11
inHg
|
0.00540269
ksi
|
12
inHg
|
0.00589385
ksi
|
13
inHg
|
0.006385
ksi
|
14
inHg
|
0.00687616
ksi
|
15
inHg
|
0.00736731
ksi
|
16
inHg
|
0.00785846
ksi
|
17
inHg
|
0.00834962
ksi
|
18
inHg
|
0.00884077
ksi
|
19
inHg
|
0.00933193
ksi
|
20
inHg
|
0.00982308
ksi
|
21
inHg
|
0.0103142
ksi
|
22
inHg
|
0.0108054
ksi
|
23
inHg
|
0.0112965
ksi
|
24
inHg
|
0.0117877
ksi
|
25
inHg
|
0.0122789
ksi
|
26
inHg
|
0.01277
ksi
|
27
inHg
|
0.0132612
ksi
|
28
inHg
|
0.0137523
ksi
|
29
inHg
|
0.0142435
ksi
|
30
inHg
|
0.0147346
ksi
|
31
inHg
|
0.0152258
ksi
|
32
inHg
|
0.0157169
ksi
|
33
inHg
|
0.0162081
ksi
|
34
inHg
|
0.0166992
ksi
|
35
inHg
|
0.0171904
ksi
|
36
inHg
|
0.0176815
ksi
|
37
inHg
|
0.0181727
ksi
|
38
inHg
|
0.0186639
ksi
|
39
inHg
|
0.019155
ksi
|
40
inHg
|
0.0196462
ksi
|
41
inHg
|
0.0201373
ksi
|
42
inHg
|
0.0206285
ksi
|
43
inHg
|
0.0211196
ksi
|
44
inHg
|
0.0216108
ksi
|
45
inHg
|
0.0221019
ksi
|
46
inHg
|
0.0225931
ksi
|
47
inHg
|
0.0230842
ksi
|
48
inHg
|
0.0235754
ksi
|
49
inHg
|
0.0240665
ksi
|
50
inHg
|
0.0245577
ksi
|
51
inHg
|
0.0250489
ksi
|
52
inHg
|
0.02554
ksi
|
53
inHg
|
0.0260312
ksi
|
54
inHg
|
0.0265223
ksi
|
55
inHg
|
0.0270135
ksi
|
56
inHg
|
0.0275046
ksi
|
57
inHg
|
0.0279958
ksi
|
58
inHg
|
0.0284869
ksi
|
59
inHg
|
0.0289781
ksi
|
60
inHg
|
0.0294692
ksi
|
61
inHg
|
0.0299604
ksi
|
62
inHg
|
0.0304515
ksi
|
63
inHg
|
0.0309427
ksi
|
64
inHg
|
0.0314339
ksi
|
65
inHg
|
0.031925
ksi
|
66
inHg
|
0.0324162
ksi
|
67
inHg
|
0.0329073
ksi
|
68
inHg
|
0.0333985
ksi
|
69
inHg
|
0.0338896
ksi
|
70
inHg
|
0.0343808
ksi
|
71
inHg
|
0.0348719
ksi
|
72
inHg
|
0.0353631
ksi
|
73
inHg
|
0.0358542
ksi
|
74
inHg
|
0.0363454
ksi
|
75
inHg
|
0.0368366
ksi
|
76
inHg
|
0.0373277
ksi
|
77
inHg
|
0.0378189
ksi
|
78
inHg
|
0.03831
ksi
|
79
inHg
|
0.0388012
ksi
|
80
inHg
|
0.0392923
ksi
|
81
inHg
|
0.0397835
ksi
|
82
inHg
|
0.0402746
ksi
|
83
inHg
|
0.0407658
ksi
|
84
inHg
|
0.0412569
ksi
|
85
inHg
|
0.0417481
ksi
|
86
inHg
|
0.0422392
ksi
|
87
inHg
|
0.0427304
ksi
|
88
inHg
|
0.0432216
ksi
|
89
inHg
|
0.0437127
ksi
|
90
inHg
|
0.0442039
ksi
|
91
inHg
|
0.044695
ksi
|
92
inHg
|
0.0451862
ksi
|
93
inHg
|
0.0456773
ksi
|
94
inHg
|
0.0461685
ksi
|
95
inHg
|
0.0466596
ksi
|
96
inHg
|
0.0471508
ksi
|
97
inHg
|
0.0476419
ksi
|
98
inHg
|
0.0481331
ksi
|
99
inHg
|
0.0486242
ksi
|
100
inHg
|
0.0491154
ksi
|
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