You just use pi 22/7 when is a multiple of 7
Why PI Must Be 22 Over 7 Or (3.14.....)?
It's not a question of why it must be, it simply is. And it's 3.14159, or 22/7. It's the relationship between the radius of a circle and it's circumference. It's a law of nature, or science, not something invented by man.