Math functions deg2rad() to convert Degree to Radian value in PHP

Convert degrees to radians

PHP trigonometric functions such as sin(), cos() and tan() work with radians. Use deg2rad() when your starting angle is in degrees.

$degrees = 60;
$radians = deg2rad($degrees);
echo $radians;

<?Php
echo deg2rad(0); // Output is 0
echo "<br>";
echo deg2rad(90); // Output  1.5707963267949
echo "<br>";
echo deg2rad(180); // Output is 3.1415926535898
echo "<br>";
echo deg2rad(270); // Output is 4.7123889803847 
?>

Syntax

float deg2rad(float $degrees);

$degrees is the angle measured in degrees. The returned value is a float in radians.

deg2rad() with round()

Use round() when you need fewer decimal places for display; keep the unrounded value for calculations when precision matters.

<?Php
echo round(deg2rad(90),2); // Output  is 1.57
?>

deg2rad() with sin() cos()

sin(), cos() and tan() accept radians. Convert degree input with deg2rad() before calling them.

<?Php
echo sin(deg2rad(90)); // Output  is 1
?>

Let us try few more examples

<?Php
echo sin(deg2rad(0)); // Output  is 0
echo "<br>";
echo round(sin(deg2rad(180))); // Output  is 0
echo "<br>";
echo sin(deg2rad(270)); // Output  is -1
echo "<br>";
echo cos(deg2rad(0)); // Output  is 1
echo "<br>";
echo cos(deg2rad(180)); // Output  is -1
echo "<br>";
echo tan(deg2rad(45)); // Output  is 1
?>

Example: Calculating Radians for Trigonometric Functions

$degrees = 90;
$radians = deg2rad($degrees);
echo "Radians: " . $radians;  // Output: Radians: 1.5708
echo "Sine of 90 degrees: " . sin($radians);  // Output: 1

Example: Calculating Angular Velocity

$degrees_per_second = 30;
$radians_per_second = deg2rad($degrees_per_second);
echo "Radians per second: " . $radians_per_second;  // Output: 0.5236

Example: Using deg2rad() in the Haversine Formula

function haversine($lat1, $lon1, $lat2, $lon2) {
    $earth_radius = 6371;  // Radius of the Earth in km
    $dLat = deg2rad($lat2 - $lat1);
    $dLon = deg2rad($lon2 - $lon1);
    
    $a = sin($dLat/2) * sin($dLat/2) +
        cos(deg2rad($lat1)) * cos(deg2rad($lat2)) * 
        sin($dLon/2) * sin($dLon/2);
    
    $c = 2 * atan2(sqrt($a), sqrt(1-$a));
    
    return $earth_radius * $c;  // Output in km
}

$distance = haversine(51.5074, -0.1278, 40.7128, -74.0060);  // London to New York
echo "Distance: " . $distance . " km";  // Output: Distance: 5570.22 km

Example: Converting an Array of Degrees to Radians

$angles = [0, 30, 45, 90, 180];
$radians = array_map('deg2rad', $angles);
print_r($radians);  // Output: Array ( [0] => 0 [1] => 0.5235987755983 [2] => 0.78539816339745 [3] => 1.5707963267949 [4] => 3.1415926535898 )

Plotting of SIN & COS curves by using PHP GD function with deg2rad()

Math Functions rad2deg() function

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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