# PHP pi() Function

PHPServer Side ProgrammingProgramming

## Definition and Usage

The pi () function returns the value of mathematical constant Π. It returns a float value 3.14159265359 which is equal to predefined constant defined in PHP - M_PI

## Syntax

pi ( void ) : float

## Parameters

This function requires no parameters

## Return Values

PHP pi() function returnsthe mathematical constant Π and is equal to predefined mathematical constant M-PI. Instead of using M_PI, we can use pi() function in mathematical expressions.

## PHP Version

This function is available in PHP versions 4.x, PHP 5.x as well as PHP 7.x.

## Example

Live Demo

Following exampleuses pi() function in calculation of area of circle.

<?php
$radius = 5; echo "area of circle with radius = " .$radius . " is " . pi()*pow(\$radius,2);
?>

## Output

This will produce following result −

area of circle with radius = 5is 78.539816339745

## Example

Live Demo

Following example uses pi() function to calculate Π/2 and Π/4. For these angles PHP has M_PI_2 and M_PI-4 predefined constants respectively .−

<?php
echo "pi/2 = " . pi()/2;
echo " M-PI_2 = " . M_PI_2 . "\n";
echo "pi/4 = " . pi()/4;
echo " M_PI_4 = ". M_PI_4;
?>

## Output

This will produce following result −

pi/2 = 1.5707963267949 M-PI_2 = 1.5707963267949
pi/4 = 0.78539816339745 M_PI_4 = 0.78539816339745

## Example

Live Demo

Using pi() function, value of 1/Π and 2/Π is calculated. These values are equivalent to M_1_PI and M_2_PI respectively;

<?php
echo "1/pi = " . 1/pi();
echo " M_1_PI = " . M_1_PI . "\n";
echo "2/pi = " . 2/pi();
echo " M_2_PI = ". M_2_PI;
?>

## Output

This will produce following result −

1/pi = 0.31830988618379 M_1_PI = 0.31830988618379
2/pi = 0.63661977236758 M_2_PI = 0.63661977236758

## Example

Live Demo

This example shows sqrt(Π) and 2/sqrt(Π) calculated using pi() function are similar to M_SQRTPI and M_2_SQRTPI.−

<?php
echo "sqrt(pi) = " . sqrt(pi());
echo " M_SQRTPI = " . M_SQRTPI . "\n";
echo "2/sqrt(pi) = " . 2/sqrt(pi());
echo " M_2_SQRTPI = ". M_2_SQRTPI;
?>

## Output

This will produce following result −

sqrt(pi) = 1.7724538509055 M_SQRTPI = 1.7724538509055
2/sqrt(pi) = 1.1283791670955 M_2_SQRTPI = 1.1283791670955