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<?php
//result: "90 degrees = 1.57079632679 radians "
$degrees = 90;
$radians = deg2rad($degrees);
echo "$degrees degrees = $radians radians ";

//result: "1.57079632679491 radians = 90 degrees"
$radians = 1.57079632679491;
$degrees = rad2deg($radians);
echo "$radians radians = $degrees degrees";
?>

The formula to convert an angle measurement in degrees (D) to radians (R) is D = R*180/pi. Fortunately, PHP comes with a function to do it for you automatically: the deg2rad( ) function or if you have a value that is already in radians, you can convert it to degrees with the rad2reg( ) function.