What is a good Cronbach's alpha?

A common rule of thumb (George & Mallery) is ≥ 0.9 excellent, ≥ 0.8 good, ≥ 0.7 acceptable, ≥ 0.6 questionable, ≥ 0.5 poor, and below 0.5 unacceptable. Very high values above 0.95 can signal redundant items.

Why is my Cronbach's alpha negative or very low?

The most common cause is a negatively worded item that has not been reverse-coded. Mark that item as reversed and recalculate. Few items or a scale measuring more than one construct can also lower alpha.

How should data be entered?

One row per respondent and one column per item, separated by commas, tabs, or spaces. You can paste directly from Excel, Google Sheets, or SPSS data view.

CRONBACH'S ALPHA CALCULATOR

Cronbach's alpha calculator for questionnaire reliability.

Paste item scores straight from Excel, Google Sheets, or SPSS. Get alpha, corrected item-total correlations, and alpha if item deleted, with reverse-coded items handled for you.

DATA

One row per respondent, one column per item

BROWSER-ONLY

ITEM SCORES (HEADER ROW OPTIONAL)

REVERSE-CODED ITEMSSCALE MIN – MAX

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Cronbach's alpha formula, interpretation, and reporting

Formula

α = (k ÷ (k − 1)) × (1 − Σσ²ᵢ ÷ σ²ₜ)

k is the number of items, σ²ᵢ is the variance of each item, and σ²ₜ is the variance of respondents' total scores. Sample variances (n − 1) are used, matching SPSS, jamovi, and R's psych package.

Interpretation (George & Mallery)

α ≥ 0.90 — Excellent
0.80 ≤ α < 0.90 — Good
0.70 ≤ α < 0.80 — Acceptable
0.60 ≤ α < 0.70 — Questionable
0.50 ≤ α < 0.60 — Poor
α < 0.50 — Unacceptable

Reverse-coded items

Negatively worded statements must be flipped before computing alpha. On a 1–5 scale the reversed score is 6 − x; in general it is (min + max) − x.

If alpha is unexpectedly low or negative, look for an item with a negative item-total correlation: it is almost always an item that still needs reverse coding.

How to report Cronbach's alpha (APA style)

Example: “The 10-item engagement scale showed good internal consistency (Cronbach's α = .84, N = 212).” APA style drops the leading zero for values that cannot exceed 1.

Report alpha separately for each subscale, not only for the full questionnaire, and mention any items removed and why.

Alpha measures internal consistency of one scale. For agreement between two raters or coders, use Cohen's kappa instead.

References

Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16(3), 297–334.
George, D., & Mallery, P. (2003). SPSS for Windows Step by Step: A Simple Guide and Reference (4th ed.). Allyn & Bacon.
Tavakol, M., & Dennick, R. (2011). Making sense of Cronbach’s alpha. International Journal of Medical Education, 2, 53–55.

Cronbach's Alpha Calculator

Check the internal consistency of a questionnaire scale from raw item scores, reverse-code negatively worded items, and see which items lower reliability.

Test reliability of a Likert-scale questionnaire for a thesis

Find items that lower alpha before the final survey

Reverse-code negatively worded items automatically

KEY FUNCTIONS

Raw Cronbach's alphaCorrected item-total correlationAlpha if item deletedReverse coding by scale minimum and maximumInterpretation band and APA-style sentence

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