Free tool, data and statistics
Cronbach’s alpha calculator
Alpha and item statistics from data pasted from Excel.
Copy the item scores of one scale from Excel or SPSS, paste them in the box, and you will get Cronbach’s alpha along with an item table. In that table each item has two numbers next to it, the corrected item–total correlation and the alpha you would get after deleting it.
Mostly scholars open this page the same evening their pilot forms come back. Suppose one college returned thirty filled forms. Your trust scale has five questions and the guide wants the reliability figure on Monday morning. SPSS is in the department lab and you are at home, so paste the scores here. If one question is dragging the trust scale down, the item table shows which one, and you can reword it before you print the next 400 forms.
Not sure the answer fits your study? WhatsApp us or call, and we’ll look at it with you.
How the tool works
Cronbach’s alpha is a measure of whether the items of a scale are moving together, as if they belong to one construct. We use the usual formula, α = k ÷ (k − 1) × (1 − sum of item variances ÷ variance of the total score), where k is how many items you have. Variances are sample variances, divided by n − 1, which is what SPSS also does. Because of that your alpha here and the SPSS Reliability Analysis output should agree till the third decimal.
For the layout, each respondent goes in one row and each item in one column. You can copy straight from Excel or from SPSS Data View, the calculator reads tab, comma and semicolon as separators. Text anywhere in the first row means it is a header, and those words become the item names. When a row has an empty cell or some word in it, that row is left out of the calculation, and just above the alpha you will see a line telling how many rows got left out. Some of our scholars type 3,5 for three and half. With tab or semicolon separator the calculator understands that comma as decimal point.
Whatever column numbers you typed in the reverse-coded box, those items it flips first. Score of 1 on a reversed item turns into 5 on a 5-point scale, a 2 turns into 4, and so on. Internally it is just scale points + 1 − old score.
After the flipping, the item statistics are worked out. To get the corrected item–total correlation, the calculator adds up all the other items and correlates your item with that total, so the item is not correlated with itself. Alpha if deleted is simply the alpha recalculated with that one item taken out. You need minimum three items for all this. If every respondent marked the same answer for one item, the table flags it, since it gives no information to the scale.
We always tell our scholars to first try five rows of three items, then only paste the real data. Type 4 5 4, then 3 3 2, 5 5 5, 2 2 3 and last 4 4 4. You should get alpha 0.939. In the item table the third item shows alpha if deleted as 0.966, higher than 0.939, so the third item is the weakest fit with the other two. How to read and write up these figures in your chapter is covered in our Cronbach’s alpha guide.
Questions scholars ask
What alpha is good enough?
Many committees are fine with 0.70 when the scale is an established one. In a pilot of a newly made scale, some guides will accept a little below that. Above roughly 0.90, check if two or three items are the same question written differently. Look at what cut-off recent papers in your area are using and cite one paper that mentions it.
My alpha is negative. What went wrong?
In almost every case we have seen, somebody forgot to flip a reverse-coded item. Go to the item table and see which item has a negative corrected item–total correlation. That is usually the one. Put that item number in the reverse-coded field and click Calculate alpha again. When that was the issue, alpha jumps up and the table starts looking normal.
How many respondents do I need?
Technically the calculator will give you a number with three complete rows. But with only 10 rows, changing one or two answers can move alpha a lot, so do not trust it much. For pilots, around 30 respondents is what most scholars collect. The alpha going in Chapter 4 has to be from the main sample data.
How do I report alpha in my thesis?
Give alpha for every scale, and mention how many items it had and the sample size. A sentence like this is enough. “The trust scale (five items) showed good internal consistency, α = .86, n = 212.” If you have dropped some item, examiners will ask which one and why, so write that also in one line.
Do my responses leave my computer?
No. All the calculation runs inside your own browser and your data is not sent anywhere. On our server we only log that the calculator was used.
Stuck on a chapter? Talk it through with us.
Call or WhatsApp, say where you are in your thesis, and we’ll tell you plainly what kind of help makes sense, if any.