What this calculator does
An average star calculator turns a breakdown of review counts, how many 1-star, 2-star, 3-star, 4-star and 5-star ratings you received, into the single overall figure shown on a product page. It is a weighted average, not a simple average of five numbers, because each star level counts once for every review left at that level.
The mistake people make is averaging the five star levels themselves, treating "1, 2, 3, 4, 5" as the dataset and getting 3.0. That ignores how many reviews sit at each level. A product with two hundred 5-star reviews and five 1-star reviews sits close to 5.0, not 3.0, because the weighting comes from the actual counts.
The formula
Multiply each star level by the number of reviews at that level, add the five results together, then divide by the total number of reviews. A 5-star review contributes five times as much to the total as a 1-star review, which is exactly how the weighting should work.
| Term | Meaning |
|---|---|
| Weighted average | An average where each value counts in proportion to how often it occurs, rather than being counted once. |
| Total reviews | The sum of the counts entered across all five star levels. |
| Star level | The 1 to 5 rating a single review was given. |
The inputs explained
| Field | What to enter |
|---|---|
| Number of 1-star reviews | How many reviews gave the lowest, 1-star rating. |
| Number of 2-star reviews | How many reviews gave a 2-star rating. |
| Number of 3-star reviews | How many reviews gave a 3-star rating. |
| Number of 4-star reviews | How many reviews gave a 4-star rating. |
| Number of 5-star reviews | How many reviews gave the top, 5-star rating. |
When to use it
Checking a displayed rating
If a storefront shows a star breakdown but you want to verify the headline average, or see how much a handful of low ratings actually dragged it down, entering the counts recomputes it directly.
Deciding how many 5-star reviews you need
Running different values for the 5-star count shows how many more top ratings would be needed to lift an average from, say, 4.0 towards 4.5, given the existing spread of other ratings.
Comparing two products fairly
A product with 20 reviews and one with 2,000 reviews can show the same rounded star average on the surface; recomputing from the actual breakdown shows how much more that average can move for the smaller sample.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does the average change as 5-star reviews pile up?
The number of 5-star reviews increases while every other star level stays the same.
| 5-star reviews | Average star rating | Share that are 5-star |
|---|---|---|
| 20 | 4.00 out of 5 | 34.5% |
| 40 | 4.26 out of 5 | 51.3% |
| 62 | 4.42 out of 5 | 62.0% |
| 100 | 4.58 out of 5 | 72.5% |
| 150 | 4.69 out of 5 | 79.8% |
| 200 | 4.76 out of 5 | 84.0% |
Questions
Why is the average not just the middle of 1 and 5?
Because it is a weighted average of actual review counts, not an average of the five possible star values. The result depends entirely on how many reviews sit at each level, which is why one product can score 4.8 and another 3.2 despite both using the same 1 to 5 scale.
Does one extra 1-star review change the average much?
It depends on the total review count. On a product with only ten reviews, one more 1-star rating can move the average noticeably. On a product with thousands of reviews, a single new rating at any level barely moves it.
Can I use this for other five-point scales, like satisfaction surveys?
Yes. The maths is the same weighted average regardless of what the 1 to 5 scale represents, so it works equally well for survey responses, employee ratings or any other five-point scoring system.
Why do platforms round the displayed average?
Most storefronts round to one decimal place, or to the nearest half star for the visual star icons, purely for display. The underlying average used to rank or sort products is normally kept to more decimal places than what is shown.
For averaging a plain list of numbers rather than a star breakdown, see the average calculator. To weight several percentages by sample size instead of star counts, see the average percentage calculator.