Cronbach’s alpha calculator
Paste item responses to check the internal consistency of a questionnaire. Get Cronbach’s alpha, corrected item–total correlations and alpha if each item is deleted.
Free and private: everything is calculated in your browser and nothing you paste is sent anywhere.
How it is calculated
- α = k ÷ (k − 1) × (1 − Σ item variances ÷ variance of the total score), where k is the number of items (Cronbach, 1951).
- Reverse-scored items are flipped first (lowest + highest − response), otherwise they pull alpha down.
- The corrected item–total correlation compares each item with the sum of the other items. Values below about 0.3 suggest an item does not fit well.
- Bands follow George and Mallery’s (2003) rule of thumb: .9 excellent, .8 good, .7 acceptable, .6 questionable, .5 poor. Alpha also rises with the number of items, so treat the bands as a guide.
Frequently asked questions
What is a good Cronbach’s alpha?
An alpha of .70 or above is usually treated as acceptable for research, .80 as good and .90 as excellent. Very high values (above .95) can mean some items are almost duplicates of each other.
Do I need to reverse items before calculating alpha?
Yes. Negatively worded items, such as the even items of the SUS, must be reversed first, or alpha will be badly underestimated. Pick the questionnaire from the list above and this is done for you.
Should I calculate alpha for each subscale?
Yes, if the questionnaire has subscales (for example UEQ or PSSUQ), report alpha for each subscale separately. A single alpha across several different constructs is hard to interpret.
How do I report Cronbach’s alpha in APA style?
For example: "Internal consistency was good (Cronbach’s α = .85)." APA style drops the leading zero for statistics that cannot exceed 1. The write-up box above gives a sentence you can copy.