{"id":1025,"date":"2026-10-14T02:16:00","date_gmt":"2026-10-14T02:16:00","guid":{"rendered":"https:\/\/freestatisticaltools.com\/blog\/?p=1025"},"modified":"2026-10-14T02:16:00","modified_gmt":"2026-10-14T02:16:00","slug":"cronbachs-alpha","status":"publish","type":"post","link":"https:\/\/freestatisticaltools.com\/blog\/cronbachs-alpha\/","title":{"rendered":"What Is a Good Cronbach’s Alpha? Interpretation, Thresholds and Reporting"},"content":{"rendered":"\n

If you have built or used a questionnaire, a supervisor or reviewer has almost certainly asked: "What is the Cronbach's alpha?"<\/em> Alpha is the most widely reported reliability coefficient in the social and health sciences. It is also widely misunderstood.<\/p>\n\n\n\n

This guide explains what alpha measures, what counts as a good value, how to improve a low alpha without cheating, when to report McDonald's omega instead, and exactly how to write it up.<\/p>\n\n\n

<\/svg><\/span>Free tool \u00b7 runs in your browser<\/span>Cronbach\u2019s Alpha Calculator<\/a>Free Cronbach\u2019s alpha calculator: reliability with 95% CI, standardized alpha, corrected item-total correlations and alpha if item deleted.<\/span><\/span>Calculate Cronbach's alpha \u2192<\/a><\/div>\n\n\n\n

What Cronbach's alpha measures<\/h2>\n\n\n\n

Cronbach's alpha (\u03b1) estimates the internal consistency<\/strong> of a set of items that are meant to measure the same construct: how strongly the items "hang together". If people who score high on one item of a job-satisfaction scale also tend to score high on the others, alpha will be high.<\/p>\n\n\n\n

Alpha depends on two things:<\/p>\n\n\n\n

    \n
  1. The average correlation between items.<\/strong> Stronger correlations give a higher alpha.<\/li>\n\n
  2. The number of items.<\/strong> More items give a higher alpha, even if the average correlation stays the same.<\/li>\n<\/ol>\n\n\n\n

    The standardized formula makes this explicit:<\/p>\n\n\n\n

    \u03b1 = (k \u00d7 r\u0304) \u00f7 (1 + (k \u2212 1) \u00d7 r\u0304)<\/code><\/p>\n\n\n\n

    where k is the number of items and r\u0304 is the mean inter-item correlation. With r\u0304 = .30, three items give \u03b1 = .56, while ten items give \u03b1 = .81.<\/p>\n\n\n\n

    What alpha is not<\/b>

    A high alpha does not<\/strong> show that a scale is unidimensional (measures only one thing), and it says nothing about validity. Ten items about two different topics can still produce \u03b1 = .80. Check dimensionality with exploratory factor analysis<\/a> or CFA<\/a>.<\/p><\/div>\n\n\n\n

    What is a good Cronbach's alpha?<\/h2>\n\n\n\n

    The most quoted guideline comes from George and Mallery (2003), building on Nunnally (1978):<\/p>\n\n\n\n

    Cronbach's alpha<\/th>Common interpretation<\/th><\/tr><\/thead>
    \u03b1 \u2265 .90<\/td>Excellent (but check for redundant items)<\/td><\/tr>
    .80 \u2264 \u03b1 < .90<\/td>Good<\/td><\/tr>
    .70 \u2264 \u03b1 < .80<\/td>Acceptable<\/td><\/tr>
    .60 \u2264 \u03b1 < .70<\/td>Questionable<\/td><\/tr>
    .50 \u2264 \u03b1 < .60<\/td>Poor<\/td><\/tr>
    \u03b1 < .50<\/td>Unacceptable<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    In practice:<\/p>\n\n\n\n