Cronbach's Alpha Calculator
Paste your item-level dataset (respondents in rows, items in columns) to compute Cronbach's alpha, number of items, number of respondents, item variances, and item-total correlations. Works for Likert-type scales and test items.
Accepted separators: comma, semicolon, tab, spaces
Cronbach's α
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Items (k)
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Respondents (n)
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Interpretation
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| Item | Mean | Variance | Item-total corr. |
|---|
Formula
Cronbach's alpha:
\( \alpha = \frac{k}{k-1} \left(1 - \frac{\sum_{i=1}^k \sigma_i^2}{\sigma_T^2} \right) \)
where:
- \( k \) = number of items
- \( \sigma_i^2 \) = variance of item i
- \( \sigma_T^2 \) = variance of total scores (sum of items) across respondents
How to read alpha
- ≥ 0.90: excellent
- 0.80 – 0.89: good
- 0.70 – 0.79: acceptable
- 0.60 – 0.69: questionable
- < 0.60: poor (consider revising items)
Tips
If an item has very low variance or negative item-total correlation, it may lower alpha. Consider removing or revising it and re-running this calculator.
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted LaTeX)
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Formula (extracted text)
Cronbach's alpha: \( \alpha = \frac{k}{k-1} \left(1 - \frac{\sum_{i=1}^k \sigma_i^2}{\sigma_T^2} \right) \) where: \( k \) = number of items \( \sigma_i^2 \) = variance of item i \( \sigma_T^2 \) = variance of total scores (sum of items) across respondents
Variables and units
- No variables provided in audit spec.
Sources (authoritative):
- NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures - FTC — Consumer advice — consumer.ftc.gov · Accessed 2026-01-19
https://consumer.ftc.gov/
Changelog
Version: 0.1.0-draft
Last code update: 2026-01-19
Last code update: 2026-01-19
0.1.0-draft · 2026-01-19
- Initial audit spec draft generated from HTML extraction (review required).
- Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
- Confirm sources are authoritative and relevant to the calculator methodology.