Test χ²     Enter observed frequencies (O), expected frequencies (E)

O separated by "," ↑   -   E separated by "," ↓                         χ²

Instead of the expected frequencies, you can put proportional values; eg. instead of 5,5,10 you can put 1,1,2.
In the following table, d.f. is the number of degrees of freedom.
examples
d.f.     5       10      25      50      75      90      95 
1       0.00393 0.0158  0.102   0.455   1.32    2.71    3.84
2       0.103   0.211   0.575   1.39    2.77    4.61    5.99
3       0.352   0.584   1.21    2.37    4.11    6.25    7.81
4       0.711   1.06    1.92    3.36    5.39    7.78    9.49
5       1.15    1.61    2.67    4.35    6.63    9.24    11.1
6       1.64    2.20    3.45    5.35    7.84    10.6    12.6
8       2.73    3.49    5.07    7.34    10.2    13.4    15.5
9       3.33    4.17    5.90    8.34    11.4    14.7    16.9
10      3.94    4.87    6.74    9.34    12.5    16.0    18.3
11      4.57    5.58    7.58    10.3    13.7    17.3    19.7
12      5.23    6.30    8.44    11.3    14.8    18.5    21.0
13      5.89    7.04    9.30    12.3    16.0    19.8    22.4
14      6.57    7.79    10.2    13.3    17.1    21.1    23.7
15      7.26    8.55    11.0    14.3    18.2    22.3    25.0
16      7.96    9.31    11.9    15.3    19.4    23.5    26.3
17      8.67    10.1    12.8    16.3    20.5    24.8    27.6
18      9.39    10.9    13.7    17.3    21.6    26.0    28.9
19      10.1    11.7    14.6    18.3    22.7    27.2    30.1
20      10.9    12.4    15.5    19.3    23.8    28.4    31.4
25      14.6    16.5    19.9    24.3    29.3    34.4    37.7
30      18.5    20.6    24.5    29.3    34.8    40.3    43.8
35      22.5    24.8    29.1    34.3    40.2    46.1    49.8
40      26.5    29.1    33.7    39.3    45.6    51.8    55.8
45      30.6    33.4    38.3    44.3    51.0    57.5    61.7
50      34.8    37.7    42.9    49.3    56.3    63.2    67.5
55      39.0    42.1    47.6    54.3    61.7    68.8    73.3
65      47.4    50.9    57.0    64.3    72.3    80.0    84.8
75      56.1    59.8    66.4    74.3    82.9    91.1    96.2
85      64.7    68.8    75.9    84.3    93.4    102     108 
100     77.9    82.4    90.1    99.3    109     118     124