A chi square is used to investigate if distributions of categorical variables vary from one another. It is a hypothesis test which is used to compare the observed values and the expected value and find the goodness of fit. This calculator will help you to find the statistics χ2 value.
In other words, chi square is the difference of the expected and observed data. It is expressed as numerical value not as ratio or percentage.
If the test gives the observed value as 40 and expected value as 25.
(40-25)2 / 25
Hence, chi square (χ2) is 9