Ūdens tvaiks ir ūdens gāzveida agregātstāvoklī. Tas rodas, ūdenim iztvaikojot vai ledum sublimējoties. Ūdens tvaiks veido daļu no hidrosfēras. Atšķirībā no citiem ūdens agregātstāvokļiem, tvaiks nav redzams. Atmosfēras augšējos slāņos, ūdens tvaikam kondensējoties, rodas mākoņi. Ja tas notiek zemes virskārtas tuvumā, tad veidojas migla.
Gaisa mitrums ir ūdens tvaika daudzums gaisā, to mēra ar higrometriem. Gaisa mitrumu ar vērtību 100% sauc par piesātinātu un tas nozīmē, ka gaisā esošā ūdens parciālspiediens ir vienāds ar maksimālo ūdens parciālspiedienu attiecīgajai temperatūrai. Pieaugot temperatūrai, pieaug maksimālais pieļaujamais ūdens tvaika daudzums gaisā. Gaisa mitrums ir robežās no 0 gramiem ūdens tvaika uz kubikmetru sausam gaisam līdz 30 gramiem ūdens tvaika uz kubikmetru, kad ūdens tvaiks ir piesātināts 30 °C.
Ūdens tvaika spiediens atkarībā no temperatūras, bāros.
°C |
0 |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9
|
0
|
0,006351
|
0,006827
|
0,007335
|
0,007876
|
0,008452
|
0,009066
|
0,00972
|
0,010411
|
0,011147
|
0,011929
|
10
|
0,01276
|
0,01364
|
0,014574
|
0,015563
|
0,01661
|
0,017719
|
0,018893
|
0,020135
|
0,021444
|
0,022831
|
20
|
0,024299
|
0,025849
|
0,027481
|
0,029194
|
0,031009
|
0,032926
|
0,034935
|
0,037056
|
0,039289
|
0,041634
|
30
|
0,044102
|
0,046702
|
0,049425
|
0,052290
|
0,055298
|
0,058459
|
0,061763
|
0,065240
|
0,068881
|
0,072694
|
40
|
0,076681
|
0,080872
|
0,085247
|
0,089825
|
0,094618
|
0,099635
|
0,104866
|
0,110342
|
0,116062
|
0,122027
|
50
|
0,128258
|
0,134764
|
0,141534
|
0,148611
|
0,155984
|
0,163662
|
0,171666
|
0,180008
|
0,188685
|
0,19772
|
60
|
0,207101
|
0,21689
|
0,227087
|
0,23759
|
0,248603
|
0,260024
|
0,271852
|
0,28419
|
0,296937
|
0,310295
|
70
|
0,324061
|
0,338336
|
0,353122
|
0,368418
|
0,384325
|
0,400844
|
0,417873
|
0,435616
|
0,453868
|
0,472835
|
80
|
0,492413
|
0,512705
|
0,533711
|
0,555431
|
0,577864
|
0,601011
|
0,624974
|
0,649753
|
0,675347
|
0,701758
|
90
|
0,728882
|
0,757025
|
0,786189
|
0,816168
|
0,847065
|
0,878879
|
0,911816
|
0,94567
|
0,980544
|
1,016743
|
100
|
1,053554
|
1,091793
|
1,131051
|
1,171533
|
1,213239
|
1,256066
|
1,300219
|
1,345596
|
1,392298
|
1,440326
|
110
|
1,489680
|
1,540359
|
1,592567
|
1,646204
|
1,701267
|
1,757861
|
1,815984
|
1,875636
|
1,936920
|
1,999836
|
120
|
2,064383
|
2,130663
|
2,198575
|
2,268323
|
2,339906
|
2,413222
|
2,488476
|
2,565565
|
2,644592
|
2,725658
|
130
|
2,808662
|
2,893705
|
2,980889
|
3,070317
|
3,162090
|
3,254882
|
3,350734
|
3,448625
|
3,549576
|
3,652565
|
140
|
3,757595
|
3,870781
|
3,974791
|
4,087977
|
4,202184
|
4,320469
|
4,440794
|
4,564177
|
4,6896
|
4,818083
|
150
|
4,949624
|
5,083205
|
5,219844
|
5,360563
|
5,503321
|
5,649138
|
5,798014
|
5,950969
|
6,105964
|
6,265037
|
160
|
6,426149
|
6,591341
|
6,760611
|
6,931921
|
7,107309
|
7,286776
|
7,469303
|
7,654888
|
7,844552
|
8,038295
|
170
|
8,235097
|
8,436998
|
8,641958
|
8,849976
|
9,063094
|
9,280290
|
9,500545
|
9,725899
|
9,955331
|
10,188842
|
180
|
10,426433
|
10,668101
|
10,913849
|
11,165715
|
11,421660
|
11,681683
|
11,945786
|
12,214986
|
12,489286
|
12,768683
|
190
|
13,052160
|
13,340735
|
13,634409
|
13,933181
|
14,237051
|
14,546021
|
14,860088
|
15,179254
|
15,503519
|
15,833902
|
200
|
16,169383
|
16,510982
|
16,857680
|
17,209477
|
17,567392
|
17,931425
|
18,301576
|
18,676825
|
19,058193
|
19,445679
|
210
|
19,839283
|
20,239006
|
20,644846
|
21,057825
|
21,475902
|
21,900097
|
22,33245
|
22,974861
|
23,21551
|
23,666217
|
220
|
24,125082
|
24,590066
|
25,061167
|
25,540426
|
26,025803
|
26,519338
|
27,018991
|
27,526802
|
28,04073
|
28,562817
|
230
|
29,093061
|
29,629423
|
30,173943
|
30,726620
|
31,286435
|
31,854408
|
32,429519
|
33,013807
|
33,502244
|
34,204817
|
240
|
34,812558
|
35,429477
|
36,053533
|
36,686767
|
37,328158
|
37,977707
|
38,636433
|
39,304337
|
39,980398
|
40,665636
|
250
|
41,359032
|
42,062625
|
42,776415
|
43,500402
|
44,224389
|
44,968770
|
45,713151
|
46,477926
|
47,242701
|
48,017673
|
260
|
48,813039
|
49,608405
|
50,413968
|
51,229728
|
52,055685
|
52,891839
|
53,748387
|
54,604935
|
55,471680
|
56,348622
|
270
|
57,245958
|
58,143294
|
59,050827
|
59,978754
|
60,906681
|
61,855002
|
62,81352
|
63,782235
|
64,761147
|
65,750256
|
280
|
66,749562
|
67,759065
|
68,788962
|
69,818859
|
70,869150
|
71,929638
|
73,000323
|
74,081205
|
75,182481
|
76,293954
|
290
|
77,415624
|
78,547491
|
79,689555
|
80,852013
|
82,024668
|
83,207520
|
84,410766
|
85,624209
|
86,847849
|
88,081686
|
300
|
89,335917
|
90,600345
|
91,885167
|
93,180186
|
94,485402
|
95,800815
|
97,136622
|
98,492823
|
99,849024
|
101,235816
|
310
|
102,622608
|
104,029794
|
105,457374
|
106,895151
|
108,343125
|
109,811493
|
111,300255
|
112,799214
|
114,318567
|
115,848117
|
320
|
117,387864
|
118,958202
|
120,538737
|
122,129469
|
123,740595
|
125,372115
|
127,013832
|
128,675943
|
130,358448
|
132,05115
|
330
|
133,764246
|
135,497736
|
137,241423
|
139,015701
|
140,800176
|
133,427745
|
144,420111
|
146,265768
|
148,121622
|
149,99787
|
340
|
151,894512
|
153,811548
|
155,738781
|
157,696605
|
159,674823
|
161,663238
|
163,682244
|
165,721644
|
167,771241
|
169,851429
|
350
|
171,952011
|
174,072987
|
176,214357
|
178,376121
|
180,558279
|
182,771028
|
185,004171
|
187,257708
|
189,317502
|
191,836161
|
360
|
194,171274
|
196,516584
|
198,902682
|
201,298977
|
203,73606
|
206,193537
|
208,671408
|
211,190067
|
213,72912
|
216,298764
|
370
|
218,909196
|
221,540022
|
224,211636
|
226,913841
|
229,656834
|
-
|
-
|
-
|
-
|
-
|