Your Google rating is an average. That is all it is. Google adds up every star anyone gave you and divides by the number of reviews. So the question "how many reviews do I need to raise my rating" has an exact answer. You can work it out on paper in one minute.
This post gives you the formula, six worked examples, and a plan for getting the reviews. It also explains why moving from 4.2 to 4.5 is easy and moving from 4.5 to 4.8 is hard.
The formula
You need three numbers:
- Count: how many reviews you have now.
- Current: your rating now, for example 4.2.
- Target: the rating you want, for example 4.5.
Google shows one decimal. A listing with a true average of 4.45 displays 4.5. So the number you actually want is the number of reviews that makes the listing say your target, and that is:
X = count × ((target − 0.05) − current) ÷ (5 − (target − 0.05))
If you want the target as a true average rather than a displayed one, use the target itself:
X = count × (target − current) ÷ (5 − target)
The first number is smaller, usually by about a third. Both are below. Every new review in these formulas is a five-star review; if some are four stars you need more of them, and the FAQ covers that.
Where the formula comes from
Your rating after X new five-star reviews is:
(count × current + 5 × X) ÷ (count + X)
Set that equal to the rating you are aiming at and solve for X. Aim at the target minus 0.05 and you get the reviews to display it; aim at the target itself and you get the reviews to average it.
Six worked examples
| Reviews now | Rating now | Target | To display it | To average it |
|---|---|---|---|---|
| 100 | 4.2 | 4.5 | 46 | 60 |
| 100 | 4.2 | 4.8 | 220 | 300 |
| 50 | 3.9 | 4.3 | 24 | 29 |
| 250 | 4.4 | 4.6 | 84 | 125 |
| 800 | 4.6 | 4.7 | 115 | 267 |
| 30 | 4.0 | 4.5 | 25 | 30 |
Here is each one written out. The first number in each is the one that changes what customers see.
Example 1. 100 reviews at 4.2, target 4.5. X = 100 × (4.45 − 4.2) ÷ (5 − 4.45) = 100 × 0.25 ÷ 0.55 = 45.5. Round up to 46. Those 46 reviews put you on 650 ÷ 146 = 4.4521, and Google prints 4.5. For a true 4.50 you would need 60, about a third more.
Example 2. 100 reviews at 4.2, target 4.8. X = 100 × 0.55 ÷ 0.25 = 220 to display 4.8; 300 for a true 4.80. Same shop, same starting point. The target moved up by 0.3 more than example 1, and the work went up nearly five times.
Example 3. 50 reviews at 3.9, target 4.3. X = 50 × 0.35 ÷ 0.75 = 23.3. Round up to 24 to display it, 29 to average it. A small shop with a low rating can move fast. Two dozen happy customers fix this.
Example 4. 250 reviews at 4.4, target 4.6. X = 250 × 0.15 ÷ 0.45 = 83.3. Round up to 84 to display it, 125 to average it. A bigger review count means more work for the same jump.
Example 5. 800 reviews at 4.6, target 4.7. X = 800 × 0.05 ÷ 0.35 = 114.3. Round up to 115 to display it, 267 to average it. One tenth of a star still costs over a hundred reviews here. That is the cost of a large count and a high target together.
Example 6. 30 reviews at 4.0, target 4.5. X = 30 × 0.45 ÷ 0.55 = 24.5. Round up to 25 to display it, 30 to average it.
Why the last half star is so expensive
Look at the bottom of either formula: what is left between your target and 5. As the target climbs, that gap shrinks, and dividing by a small number gives a big answer.
- Target 4.5: you divide by 0.5.
- Target 4.7: you divide by 0.3.
- Target 4.8: you divide by 0.2.
- Target 4.9: you divide by 0.1.
Going from 4.8 to 4.9 costs the same as going from 4.2 to 4.8 with the same count. Most shops do not need to be there. Pick a target you can reach in three to six months. Then set the next one.
Two things the formula does not tell you
Google rounds the number it shows. Google displays your rating to one decimal place. A true average of 4.46 and a true average of 4.54 both show as 4.5. Aim a little past your target so a few new four-star reviews do not pull the display back down.
Old reviews count the same as new ones. A one-star review from 2019 still pulls your average down today. You cannot remove it unless it breaks Google's rules. The only fix is more good reviews.
How to get the reviews
The formula tells you the number. Getting there is a habit, not a trick.
Ask every customer. Do not pick the happy ones. Google's content rules say you must not selectively ask only happy customers or discourage negative reviews. You can read the policy at Google's user-contributed content policy. Asking everyone is also better math. Most people who like your shop never think to leave a review. Asking them is where the five stars come from.
Ask soon after the visit. The same day or the next morning works best. A week later, they have forgotten what they ate.
Make it one tap. Send a direct link to your Google review form. Do not send a link to your listing and hope they find the button.
Reply to every review. A reply shows the next reader you care. It also gives you a reason to read your reviews every week.
What KANJIN does here
KANJIN is a free back office for cafes, salons and small shops. Two pieces help with reviews.
On the Free plan, Review replies drafts a reply to each Google review. It uses your own free Gemini key, and the drafts stay on your device. You read, edit and post.
On the Paid plan ($39 a month per location, cancel any time), KANJIN sends an automatic Google review request email after a visit. It asks every customer. It never checks the rating first and never hides the form from unhappy customers. Billing is not live yet, so early access is free.
Frequently asked questions
What if the new reviews are not all five stars? Then you need more of them. If your new reviews average 4.7 instead of 5, replace the 5 in the formula with 4.7. Example 1 becomes 100 × 0.3 ÷ (4.7 − 4.5) = 150 reviews instead of 60. This is why asking everyone, and treating everyone well, matters more than any trick.
Can I just delete the bad reviews? No. You can flag a review that breaks Google's rules, for example spam or a review from someone who never visited. Google decides. A review from a real customer who had a bad day stays. The formula is the honest way up.
Does the total number of reviews matter as well as the rating? Yes. A 4.6 with 400 reviews reads as more trustworthy than a 4.9 with 12. Do not stop asking once you hit your target. New reviews also show Google and your customers that the shop is still open and still good.
How long should this take? Divide the number you need by the reviews you get each month. If you need 60 and you get 10 a month, plan for six months. If that is too slow, ask more people, not different people.
Work out your own number
Put your own count, rating and target into the free Review gap calculator. It gives you the number of five-star reviews you need and shows how it changes as you move the target. When you are ready to ask every customer automatically, the Paid plan does that for $39 a month per location.