What pi is
Pi is the distance around any circle divided by its width. It is the same for every circle, about 3.1415926536.
It cannot be written exactly as a fraction or a finite decimal, so every value you see is a rounded one.
The multiples that matter
2 pi is the number of radians in a full turn, about 6.2831853072. Half of pi is a right angle, about 1.5707963268.
Pi squared is about 9.8696044011 and the square root of pi is about 1.7724538509. Both appear in the normal distribution.
How precise you can be
This page shows up to 15 decimal places, which is as far as a browser's arithmetic stays exact.
More digits would look precise without being correct. For engineering, 3.14159 is usually enough; for mental arithmetic, 3.14 or 22/7 will do.
Inputs for the pi calculator
Decimal places
How many digits after the point to show, from 1 to 15.
CALCULATOR QUESTIONS
Pi calculator questions
What is pi to 10 decimal places?
3.1415926536.
What is 2 pi?
About 6.2831853072, the number of radians in a full circle.
Can pi be written as a fraction?
Not exactly. 22/7 is a close approximation, about 0.04% too large.
Why does the page stop at 15 places?
That is the limit of exact decimal arithmetic in the browser. Beyond it, extra digits would be noise.