Cronbach's alpha calculator

Scale reliability: internal consistency. Enter item scores — get α

Cronbach's alpha (α) — measure of internal consistency of a scale. How well items hang together; α from 0 to 1.

FAQ about Cronbach's alpha

Enter survey data

Rows = respondents, numbers in each row = item scores (space or comma separated)

Example: 3 4 5 4 3 (one respondent, 5 items). Paste from Excel: one row = one respondent.

Assumptions and limitations

α = (k / (k − 1)) × (1 − Σσ²ᵢ / σ²ₜ), where k = number of items, σ²ᵢ = variance per item, σ²ₜ = variance of total score.
Rows with different numbers of values are padded to minimum length (extra columns dropped).

Cronbach's α

—

Enter data

In SurveyNinja, NPS, CSAT and more are calculated automatically. Create a survey in 5 minutes and get real-time analytics.

Start free

Data is not stored — calculation runs in your browser.

Scale reliability

What α measures

Internal consistency: how well scale items correlate with each other and with the total score. High α — items "point in the same direction".

Norms

α < 0.5 — unacceptable; 0.5–0.6 — low; 0.6–0.7 — acceptable; 0.7–0.8 — good; 0.8–0.9 — very good; > 0.9 — excellent (for surveys 0.7+ is often enough).

Limitations

Alpha depends on number of items: with few k it is underestimated. For dichotomous items KR-20 is sometimes used; for continuous — Cronbach's alpha.

When to use

Before using a total scale score (NPS, satisfaction across several items). If α is low — revise or shorten the scale.

Cronbach's alpha calculation examples

1 Consistent scale

Scale of 5 items, 4 respondents. Line 1: 3 4 5 4 3. Line 2: 2 3 4 3 2. Line 3: 4 5 5 4 4. Line 4: 3 3 4 4 3.

Result: α will be around 0.85–0.95 — "good" or "very good". Scale items are consistent; total score can be used.

2 Outlier item

Scale of 3 items, 6 respondents. Third item worded in reverse or measures something else. Rows: 4 4 1, 5 5 2, 3 4 1, 4 5 2, 5 4 1, 4 4 2.

Result: α will be noticeably lower (e.g. 0.4–0.6). Revise, recode (reverse), or drop that item.

3 Short scale (2 items)

2 items, 8 respondents. Rows: 4 4, 3 3, 5 5, 4 5, 3 4, 5 4, 4 4, 3 3.

Result: α can be 0.8+ with good consistency. With few k the formula "penalizes" — interpret with number of items in mind.

4 Satisfaction (1–5 scale, 10 people)

5 items on service quality. Enter 10 rows of scores (e.g. from survey export). Typical rows: 4 4 5 4 3, 5 5 4 5 4, 3 3 4 3 4, etc.

Result: if α ≥ 0.7, the scale total can be used in reports; if lower — check reverse-worded and weak items.

5 One respondent — not allowed

One row: 3 4 5 4 3. n = 1.

Result: calculator will not compute α — you need at least 2 respondents and 2 items. For stable estimates, n ≥ 30 is recommended.

6 Many items, few respondents

Scale of 10 items, only 5 respondents. α is often underestimated due to small n.

Result: with n < 10 interpretation is unreliable. First collect at least 30 responses, then compute α.

Interpreting α

α (range)

Interpretation

< 0,5

Unacceptable — scale unreliable

0,5 – 0,6

Low consistency

0,6 – 0,7

Acceptable for research

0,7 – 0,8

Good — scale suitable for use

0,8 – 0,9

Very good

> 0,9

Excellent — high internal consistency

For surveys α ≥ 0.7 is often enough. With few items (k) or respondents (n), α may be underestimated.

Frequently asked questions about Cronbach's alpha

What is Cronbach's alpha?

Coefficient of internal consistency of a scale: how well items measure the same construct. Values 0 to 1; 0.7+ is usually considered acceptable.

How to enter data?

One row per respondent. Numbers in the row are item scores, space or comma separated. You can paste from Excel (columns = items).

Why is alpha low?

Too few items or respondents; items measure different things; reverse-worded items not recoded. Check item–total correlations and drop weak items.

How does alpha differ from KR-20?

KR-20 is for dichotomous items (0/1). Cronbach's alpha is for continuous scores (1–5, 1–7 scales, etc.).

How many respondents for α?

At least 30 recommended; 100+ for stable estimates. With small n the result can vary a lot.

All calculators

Automate your metrics