Hello aspirant ,Hope you are doing well

Actually there was no definite rule that how much plagiarism is allowed .It varies from publisher to publisher and also it depends upon the length of the blog.Generally a blog will get access to publish only when it's plagiarism is less than 15%.

WAYS TO AVOID PLAGIARISM

1.Rephrase your content

2.Use Quotations

3.Cite Sources

4.Use Plagiarism checkers like Turnitin etc..

Hope this helps you

ALL THE BEST