How many 5 star reviews does it take to cancel out a 1 star review?

The maths is unforgiving. A one-star review sits 4 points below a five-star average, and every five-star you add claws back only 0.2 of a point of headroom against it. Recovering to a 4.8 average therefore takes 19 five-stars for each one-star. Recovering to 4.5 takes 7. A single one-star on an otherwise perfect record permanently caps you below 4.98, however many fives follow.

How much it hurts depends entirely on how many reviews you already hold. On a profile with 10 reviews, one one-star drops a perfect 5.0 to about 4.64, a fall the customer sees instantly. On a profile with 100 reviews, the same review lands you on 4.96 and the displayed rating does not move at all. Same review, different armour.

This is why the productive response to a bad review is almost never about that review. Disputing it, replying angrily or begging the customer to change it are all low-percentage plays. Adding 20 genuine reviews from the customers who were delighted is a high-percentage play that also builds the buffer against the next one.

The exception is a review that breaks Google's rules: written by someone who was never a customer, aimed at the wrong business, or containing abuse. Those are worth reporting through your Business Profile because removal deletes the damage rather than diluting it.

Whatever you do, reply publicly and calmly. Future customers read the one-star and then read your answer, and a measured reply that states your side and offers to put things right often neutralises more damage than the star itself caused.