The hectopascal (hPa) is a commonly used unit for measuring atmospheric pressure, especially in meteorology. One hPa is equivalent to 100 pascals, making it a preferred measurement over pascals due to the convenient scale. Interestingly, 1 hPa is also equivalent to 1 millibar, a unit that was widely used before the adoption of the hectopascal. This equivalence makes it easy for transitioning instruments and readings in weather maps and reports.
Hectopascals play a crucial role in understanding atmospheric conditions, such as weather forecasting and studying phenomena like hurricanes or cyclones. Typically, sea-level pressure is around 1013 hPa, and deviations from this can indicate changing weather patterns, with lower pressures often associated with storm systems. This connection makes the hPa unit vital for predicting and understanding weather events globally.
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.
Hectopascals | Inches of mercury |
---|---|
0
hPa
|
0
inHg
|
10
hPa
|
0.2953
inHg
|
20
hPa
|
0.5906
inHg
|
30
hPa
|
0.885899
inHg
|
40
hPa
|
1.1812
inHg
|
50
hPa
|
1.4765
inHg
|
60
hPa
|
1.7718
inHg
|
70
hPa
|
2.0671
inHg
|
80
hPa
|
2.3624
inHg
|
90
hPa
|
2.6577
inHg
|
100
hPa
|
2.953
inHg
|
110
hPa
|
3.2483
inHg
|
120
hPa
|
3.5436
inHg
|
130
hPa
|
3.8389
inHg
|
140
hPa
|
4.1342
inHg
|
150
hPa
|
4.4295
inHg
|
160
hPa
|
4.7248
inHg
|
170
hPa
|
5.0201
inHg
|
180
hPa
|
5.3154
inHg
|
190
hPa
|
5.6107
inHg
|
200
hPa
|
5.906
inHg
|
210
hPa
|
6.2013
inHg
|
220
hPa
|
6.4966
inHg
|
230
hPa
|
6.7919
inHg
|
240
hPa
|
7.0872
inHg
|
250
hPa
|
7.3825
inHg
|
260
hPa
|
7.67779
inHg
|
270
hPa
|
7.97309
inHg
|
280
hPa
|
8.26839
inHg
|
290
hPa
|
8.56369
inHg
|
300
hPa
|
8.85899
inHg
|
310
hPa
|
9.15429
inHg
|
320
hPa
|
9.44959
inHg
|
330
hPa
|
9.74489
inHg
|
340
hPa
|
10.04019
inHg
|
350
hPa
|
10.33549
inHg
|
360
hPa
|
10.63079
inHg
|
370
hPa
|
10.92609
inHg
|
380
hPa
|
11.22139
inHg
|
390
hPa
|
11.51669
inHg
|
400
hPa
|
11.81199
inHg
|
410
hPa
|
12.10729
inHg
|
420
hPa
|
12.40259
inHg
|
430
hPa
|
12.69789
inHg
|
440
hPa
|
12.99319
inHg
|
450
hPa
|
13.28849
inHg
|
460
hPa
|
13.58379
inHg
|
470
hPa
|
13.87909
inHg
|
480
hPa
|
14.17439
inHg
|
490
hPa
|
14.46969
inHg
|
500
hPa
|
14.76499
inHg
|
510
hPa
|
15.06029
inHg
|
520
hPa
|
15.35559
inHg
|
530
hPa
|
15.65089
inHg
|
540
hPa
|
15.94619
inHg
|
550
hPa
|
16.24149
inHg
|
560
hPa
|
16.53679
inHg
|
570
hPa
|
16.83209
inHg
|
580
hPa
|
17.12739
inHg
|
590
hPa
|
17.42269
inHg
|
600
hPa
|
17.71799
inHg
|
610
hPa
|
18.01329
inHg
|
620
hPa
|
18.30859
inHg
|
630
hPa
|
18.60389
inHg
|
640
hPa
|
18.89919
inHg
|
650
hPa
|
19.19449
inHg
|
660
hPa
|
19.48979
inHg
|
670
hPa
|
19.78509
inHg
|
680
hPa
|
20.08039
inHg
|
690
hPa
|
20.37569
inHg
|
700
hPa
|
20.67099
inHg
|
710
hPa
|
20.96629
inHg
|
720
hPa
|
21.26159
inHg
|
730
hPa
|
21.55689
inHg
|
740
hPa
|
21.85219
inHg
|
750
hPa
|
22.14749
inHg
|
760
hPa
|
22.44279
inHg
|
770
hPa
|
22.73809
inHg
|
780
hPa
|
23.03338
inHg
|
790
hPa
|
23.32868
inHg
|
800
hPa
|
23.62398
inHg
|
810
hPa
|
23.91928
inHg
|
820
hPa
|
24.21458
inHg
|
830
hPa
|
24.50988
inHg
|
840
hPa
|
24.80518
inHg
|
850
hPa
|
25.10048
inHg
|
860
hPa
|
25.39578
inHg
|
870
hPa
|
25.69108
inHg
|
880
hPa
|
25.98638
inHg
|
890
hPa
|
26.28168
inHg
|
900
hPa
|
26.57698
inHg
|
910
hPa
|
26.87228
inHg
|
920
hPa
|
27.16758
inHg
|
930
hPa
|
27.46288
inHg
|
940
hPa
|
27.75818
inHg
|
950
hPa
|
28.05348
inHg
|
960
hPa
|
28.34878
inHg
|
970
hPa
|
28.64408
inHg
|
980
hPa
|
28.93938
inHg
|
990
hPa
|
29.23468
inHg
|
1000
hPa
|
29.52998
inHg
|
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