Cronbach's Alpha Calculator
Do Your Survey Items Measure the Same Thing?
Before a multi-item questionnaire — a satisfaction survey, a personality inventory, a symptom checklist — can be trusted, its internal consistency needs checking. Cronbach's alpha measures how closely a set of items hang together as a group, based on the idea that if items are truly tapping the same underlying construct, respondents who score high on one item should tend to score high on the others too.
The Formula
where k = number of items, item variance is computed per column, total score variance is computed on the summed score per respondent
Worked Example
Five respondents rating four items on a 1–5 scale:
| Respondent | Item 1 | Item 2 | Item 3 | Item 4 | Total |
|---|---|---|---|---|---|
| 1 | 4 | 5 | 3 | 4 | 16 |
| 2 | 3 | 4 | 4 | 3 | 14 |
| 3 | 5 | 5 | 4 | 5 | 19 |
| 4 | 2 | 3 | 3 | 2 | 10 |
| 5 | 4 | 4 | 5 | 4 | 17 |
Sum of item variances = 3.20, total score variance = 9.36, giving α = 0.8775.
Interpreting Alpha
| Alpha range | Interpretation |
|---|---|
| ≥ 0.90 | Excellent internal consistency |
| 0.80 – 0.89 | Good internal consistency |
| 0.70 – 0.79 | Acceptable internal consistency |
| 0.60 – 0.69 | Questionable internal consistency |
| 0.50 – 0.59 | Poor internal consistency |
| < 0.50 | Unacceptable internal consistency |
Bands taken directly from the calculator's classification logic, consistent with widely cited social-science conventions.
Where This Calculation Matters
- Survey and scale development — before publishing results based on a multi-item scale, researchers check alpha to confirm the items reliably measure a single construct.
- Psychometric validation — standardized tests and clinical assessment tools report alpha as a required reliability statistic.
- Trimming weak items — a low alpha often points to specific items that don't correlate well with the rest and should be revised or dropped.
How to Use This Calculator
- Enter one respondent per line, with comma-separated item scores for that respondent.
- Provide at least 2 respondents and at least 2 items (columns), with every row having the same number of scores.
- Select Calculate to get Cronbach's alpha and its reliability interpretation.
Related Calculations
To check spread within a single item's scores, see the Standard Deviation Calculator. For the relationship between two specific items, use the Correlation Calculator.