The formula
How Google calculates your star rating and how to change it
Your Google rating is a simple arithmetic mean: the sum of all star ratings divided by total review count. A new 5-star review adds 5 to the numerator and 1 to the denominator. The change in your average depends on the gap between the new rating and your current average.
The formula: New reviews needed = (Target rating times (Current reviews plus X) minus (Current rating times Current reviews)) divided by (5 minus Target rating). The Google review rating calculator solves this instantly for your specific numbers.
Examples: 20 reviews at 3.5 stars wanting 4.0 stars needs 10 new 5-star reviews. 30 reviews at 4.0 stars wanting 4.5 stars needs 15 new 5-star reviews. 10 reviews at 3.0 stars wanting 4.5 stars needs 30 new 5-star reviews.