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 torr is a unit of pressure named after the Italian physicist Evangelista Torricelli, who invented the barometer in the 17th century. It is defined as 1/760th of an atmosphere, approximating the pressure exerted by a one-millimeter column of mercury at 0 degrees Celsius. What makes the torr particularly interesting is its practical use in fields like vacuum technology and weather forecasting, where precise measurements of atmospheric pressure are crucial.
The legacy of Torricelli’s work is integral to meteorology and physics, as it opened paths for understanding atmospheric pressure. Beyond scientific circles, the torr is a reminder of human ingenuity in unraveling atmospheric mysteries and continues to play a vital role in today’s scientific advancements.
Inches of mercury | Torr |
---|---|
0
inHg
|
0
torr
|
1
inHg
|
25.40001
torr
|
2
inHg
|
50.80001
torr
|
3
inHg
|
76.20002
torr
|
4
inHg
|
101.60002
torr
|
5
inHg
|
127.00003
torr
|
6
inHg
|
152.40004
torr
|
7
inHg
|
177.80004
torr
|
8
inHg
|
203.20005
torr
|
9
inHg
|
228.60005
torr
|
10
inHg
|
254.00006
torr
|
11
inHg
|
279.40007
torr
|
12
inHg
|
304.80007
torr
|
13
inHg
|
330.20008
torr
|
14
inHg
|
355.60008
torr
|
15
inHg
|
381.00009
torr
|
16
inHg
|
406.4001
torr
|
17
inHg
|
431.8001
torr
|
18
inHg
|
457.20011
torr
|
19
inHg
|
482.60011
torr
|
20
inHg
|
508.00012
torr
|
21
inHg
|
533.40013
torr
|
22
inHg
|
558.80013
torr
|
23
inHg
|
584.20014
torr
|
24
inHg
|
609.60014
torr
|
25
inHg
|
635.00015
torr
|
26
inHg
|
660.40016
torr
|
27
inHg
|
685.80016
torr
|
28
inHg
|
711.20017
torr
|
29
inHg
|
736.60017
torr
|
30
inHg
|
762.00018
torr
|
31
inHg
|
787.40018
torr
|
32
inHg
|
812.80019
torr
|
33
inHg
|
838.2002
torr
|
34
inHg
|
863.6002
torr
|
35
inHg
|
889.00021
torr
|
36
inHg
|
914.40021
torr
|
37
inHg
|
939.80022
torr
|
38
inHg
|
965.20023
torr
|
39
inHg
|
990.60023
torr
|
40
inHg
|
1016.00024
torr
|
41
inHg
|
1041.40024
torr
|
42
inHg
|
1066.80025
torr
|
43
inHg
|
1092.20026
torr
|
44
inHg
|
1117.60026
torr
|
45
inHg
|
1143.00027
torr
|
46
inHg
|
1168.40027
torr
|
47
inHg
|
1193.80028
torr
|
48
inHg
|
1219.20029
torr
|
49
inHg
|
1244.60029
torr
|
50
inHg
|
1270.0003
torr
|
51
inHg
|
1295.4003
torr
|
52
inHg
|
1320.80031
torr
|
53
inHg
|
1346.20032
torr
|
54
inHg
|
1371.60032
torr
|
55
inHg
|
1397.00033
torr
|
56
inHg
|
1422.40033
torr
|
57
inHg
|
1447.80034
torr
|
58
inHg
|
1473.20035
torr
|
59
inHg
|
1498.60035
torr
|
60
inHg
|
1524.00036
torr
|
61
inHg
|
1549.40036
torr
|
62
inHg
|
1574.80037
torr
|
63
inHg
|
1600.20038
torr
|
64
inHg
|
1625.60038
torr
|
65
inHg
|
1651.00039
torr
|
66
inHg
|
1676.40039
torr
|
67
inHg
|
1701.8004
torr
|
68
inHg
|
1727.20041
torr
|
69
inHg
|
1752.60041
torr
|
70
inHg
|
1778.00042
torr
|
71
inHg
|
1803.40042
torr
|
72
inHg
|
1828.80043
torr
|
73
inHg
|
1854.20044
torr
|
74
inHg
|
1879.60044
torr
|
75
inHg
|
1905.00045
torr
|
76
inHg
|
1930.40045
torr
|
77
inHg
|
1955.80046
torr
|
78
inHg
|
1981.20047
torr
|
79
inHg
|
2006.60047
torr
|
80
inHg
|
2032.00048
torr
|
81
inHg
|
2057.40048
torr
|
82
inHg
|
2082.80049
torr
|
83
inHg
|
2108.2005
torr
|
84
inHg
|
2133.6005
torr
|
85
inHg
|
2159.00051
torr
|
86
inHg
|
2184.40051
torr
|
87
inHg
|
2209.80052
torr
|
88
inHg
|
2235.20052
torr
|
89
inHg
|
2260.60053
torr
|
90
inHg
|
2286.00054
torr
|
91
inHg
|
2311.40054
torr
|
92
inHg
|
2336.80055
torr
|
93
inHg
|
2362.20055
torr
|
94
inHg
|
2387.60056
torr
|
95
inHg
|
2413.00057
torr
|
96
inHg
|
2438.40057
torr
|
97
inHg
|
2463.80058
torr
|
98
inHg
|
2489.20058
torr
|
99
inHg
|
2514.60059
torr
|
100
inHg
|
2540.0006
torr
|
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