Google’s ad says SSL certificate impacts SEO. It will not be possible to accurately determine the weight of this factor. Google calculates the position of each site individually, and it depends on several hundred factors.

Switching to HTTPS will not help you get the site to the first line in Google. However, when combined with other factors, an SSL certificate can affect search rankings. If two sites have the same scores on other ranking factors, then switching to HTTPS can help you climb in SERPs. Such high competition only happens on the first pages of Google.