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Water Vapor Pressure Table

Saturation vapor pressure of water from −40 °C to 150 °C. Read it the other way round and it is also the boiling point of water at each pressure — for any other value use the boiling point under vacuum calculator. Values are calculated with the IAPWS saturation equations for water and the Murphy–Koop equation for ice.

Chart of the boiling point of water versus absolute pressure from 0.6 to 101.3 kPa, with a secondary inches-of-mercury vacuum scale and marked points such as 81 °C at 50 kPa and 20 °C at 2.3 kPa.
Boiling point of water vs. vacuum pressure. Boiling point of water under vacuum. Read absolute pressure on the bottom axis or sea-level inHg vacuum on the top axis.
Use this diagram

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°C°FkPambar TorrpsiainHg abs
-40 * -40.0 0.01284 0.1284 0.09634 0.001863 0.003793
-35 * -31.0 0.02235 0.2235 0.1676 0.003241 0.0066
-30 * -22.0 0.03801 0.3801 0.2851 0.005513 0.01122
-25 * -13.0 0.06328 0.6328 0.4747 0.009179 0.01869
-20 * -4.0 0.1033 1.033 0.7745 0.01498 0.03049
-15 * 5.0 0.1653 1.653 1.24 0.02397 0.04881
-10 * 14.0 0.2599 2.599 1.949 0.03769 0.07675
-5 * 23.0 0.4018 4.018 3.013 0.05827 0.1186
0 * 32.0 0.6112 6.112 4.584 0.08864 0.1805
1 33.8 0.6571 6.571 4.928 0.0953 0.194
2 35.6 0.706 7.06 5.295 0.1024 0.2085
3 37.4 0.7581 7.581 5.686 0.1099 0.2239
4 39.2 0.8135 8.135 6.102 0.118 0.2402
5 41.0 0.8725 8.725 6.545 0.1265 0.2577
6 42.8 0.9353 9.353 7.015 0.1357 0.2762
7 44.6 1.002 10.02 7.516 0.1453 0.2959
8 46.4 1.073 10.73 8.048 0.1556 0.3168
9 48.2 1.148 11.48 8.612 0.1665 0.3391
10 50.0 1.228 12.28 9.212 0.1781 0.3627
11 51.8 1.313 13.13 9.847 0.1904 0.3877
12 53.6 1.403 14.03 10.52 0.2035 0.4142
13 55.4 1.498 14.98 11.24 0.2173 0.4424
14 57.2 1.599 15.99 11.99 0.2319 0.4721
15 59.0 1.706 17.06 12.79 0.2474 0.5037
16 60.8 1.819 18.19 13.64 0.2638 0.5371
17 62.6 1.938 19.38 14.54 0.2811 0.5724
18 64.4 2.065 20.65 15.49 0.2994 0.6097
19 66.2 2.198 21.98 16.49 0.3188 0.6491
20 68.0 2.339 23.39 17.55 0.3393 0.6908
21 69.8 2.488 24.88 18.66 0.3609 0.7347
22 71.6 2.645 26.45 19.84 0.3837 0.7811
23 73.4 2.811 28.11 21.08 0.4077 0.8301
24 75.2 2.986 29.86 22.39 0.433 0.8817
25 77.0 3.17 31.7 23.78 0.4597 0.936
26 78.8 3.364 33.64 25.23 0.4879 0.9933
27 80.6 3.568 35.68 26.76 0.5175 1.054
28 82.4 3.783 37.83 28.37 0.5487 1.117
29 84.2 4.009 40.09 30.07 0.5815 1.184
30 86.0 4.247 42.47 31.85 0.616 1.254
31 87.8 4.497 44.97 33.73 0.6522 1.328
32 89.6 4.76 47.6 35.7 0.6903 1.405
33 91.4 5.035 50.35 37.77 0.7303 1.487
34 93.2 5.325 53.25 39.94 0.7723 1.572
35 95.0 5.629 56.29 42.22 0.8164 1.662
36 96.8 5.948 59.48 44.61 0.8627 1.756
37 98.6 6.282 62.82 47.12 0.9112 1.855
38 100.4 6.633 66.33 49.75 0.962 1.959
39 102.2 7 70 52.51 1.015 2.067
40 104.0 7.385 73.85 55.39 1.071 2.181
41 105.8 7.788 77.88 58.42 1.13 2.3
42 107.6 8.21 82.1 61.58 1.191 2.424
43 109.4 8.651 86.51 64.89 1.255 2.555
44 111.2 9.113 91.13 68.35 1.322 2.691
45 113.0 9.595 95.95 71.97 1.392 2.834
46 114.8 10.1 101 75.75 1.465 2.982
47 116.6 10.63 106.3 79.71 1.541 3.138
48 118.4 11.18 111.8 83.84 1.621 3.301
49 120.2 11.75 117.5 88.15 1.705 3.47
50 122.0 12.35 123.5 92.65 1.792 3.648
51 123.8 12.98 129.8 97.35 1.882 3.833
52 125.6 13.63 136.3 102.2 1.977 4.025
53 127.4 14.31 143.1 107.4 2.076 4.227
54 129.2 15.02 150.2 112.7 2.179 4.436
55 131.0 15.76 157.6 118.2 2.286 4.655
56 132.8 16.53 165.3 124 2.398 4.882
57 134.6 17.34 173.4 130 2.514 5.119
58 136.4 18.17 181.7 136.3 2.636 5.366
59 138.2 19.04 190.4 142.8 2.762 5.623
60 140.0 19.95 199.5 149.6 2.893 5.89
61 141.8 20.89 208.9 156.7 3.03 6.168
62 143.6 21.87 218.7 164 3.172 6.458
63 145.4 22.89 228.9 171.7 3.319 6.758
64 147.2 23.94 239.4 179.6 3.473 7.071
65 149.0 25.04 250.4 187.8 3.632 7.395
66 150.8 26.18 261.8 196.4 3.798 7.732
67 152.6 27.37 273.7 205.3 3.97 8.082
68 154.4 28.6 286 214.5 4.148 8.446
69 156.2 29.88 298.8 224.1 4.333 8.823
70 158.0 31.2 312 234 4.525 9.214
71 159.8 32.58 325.8 244.3 4.725 9.62
72 161.6 34 340 255 4.932 10.04
73 163.4 35.48 354.8 266.1 5.146 10.48
74 165.2 37.01 370.1 277.6 5.368 10.93
75 167.0 38.6 386 289.5 5.598 11.4
76 168.8 40.24 402.4 301.8 5.836 11.88
77 170.6 41.94 419.4 314.6 6.083 12.39
78 172.4 43.7 437 327.8 6.339 12.91
79 174.2 45.53 455.3 341.5 6.603 13.44
80 176.0 47.42 474.2 355.6 6.877 14
81 177.8 49.37 493.7 370.3 7.16 14.58
82 179.6 51.39 513.9 385.4 7.453 15.17
83 181.4 53.48 534.8 401.1 7.756 15.79
84 183.2 55.64 556.4 417.3 8.069 16.43
85 185.0 57.87 578.7 434 8.393 17.09
86 186.8 60.17 601.7 451.3 8.728 17.77
87 188.6 62.56 625.6 469.2 9.073 18.47
88 190.4 65.02 650.2 487.7 9.43 19.2
89 192.2 67.56 675.6 506.7 9.799 19.95
90 194.0 70.18 701.8 526.4 10.18 20.72
91 195.8 72.89 728.9 546.7 10.57 21.52
92 197.6 75.69 756.9 567.7 10.98 22.35
93 199.4 78.57 785.7 589.3 11.4 23.2
94 201.2 81.54 815.4 611.6 11.83 24.08
95 203.0 84.61 846.1 634.6 12.27 24.99
96 204.8 87.77 877.7 658.3 12.73 25.92
97 206.6 91.03 910.3 682.8 13.2 26.88
98 208.4 94.39 943.9 708 13.69 27.87
99 210.2 97.85 978.5 733.9 14.19 28.9
100 212.0 101.4 1,014 760.7 14.71 29.95
105 221.0 120.9 1,209 906.8 17.54 35.7
110 230.0 143.4 1,434 1,075 20.8 42.34
115 239.0 169.2 1,692 1,269 24.54 49.96
120 248.0 198.7 1,987 1,490 28.81 58.67
125 257.0 232.2 2,322 1,742 33.68 68.58
130 266.0 270.3 2,703 2,027 39.2 79.81
135 275.0 313.2 3,132 2,349 45.43 92.5
140 284.0 361.5 3,615 2,712 52.44 106.8
145 293.0 415.7 4,157 3,118 60.29 122.7
150 302.0 476.2 4,762 3,571 69.06 140.6

* Below 0.01 °C (the triple point, 611.657 Pa) values are the sublimation pressure over ice.

References & further reading

  1. IAPWS. SR1-86(1992): Revised Supplementary Release on Saturation Properties of Ordinary Water Substance. International Association for the Properties of Water and Steam. Saturation vapour pressure equation used for liquid water.
  2. W. Wagner & A. Pruss. The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use. J. Phys. Chem. Ref. Data 31, 387 (2002). Reference equation of state for water.
  3. D. M. Murphy & T. Koop. Review of the vapour pressures of ice and supercooled water for atmospheric applications. Q. J. R. Meteorol. Soc. 131, 1539 (2005). Sublimation pressure over ice below 0.01 °C.

Frequently asked questions

What is the vapor pressure of water at 20 °C?

About 2.339 kPa (23.39 mbar, 17.54 Torr, 0.339 psia). At 25 °C it is 3.17 kPa, and at 100 °C it reaches 101.3 kPa — atmospheric pressure — which is why water boils at 100 °C at sea level.

Why does vapor pressure matter in vacuum systems?

Water vapor is the dominant gas load in most vacuum systems below about 20 mbar. A chamber cannot be pumped below the vapor pressure of any liquid water inside it until the water has evaporated, and oil-sealed pumps can condense water into their oil if the vapor is not handled with gas ballast.

How is the vapor pressure of water calculated here?

Above the triple point (0.01 °C) the table uses the IAPWS Wagner–Pruss saturation equation for liquid water; below it, the Murphy–Koop sublimation equation for ice. Both agree with reference tables to better than 0.1 %.

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