PHP atan2() Function

August 4, 2025
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The atan2() function in PHP returns the arc tangent of two variables, y and x, representing coordinates.
It calculates the angle (in radians) between the positive X-axis and the point (x, y).
Unlike atan(), it correctly handles the signs of both arguments to determine the correct quadrant.
It returns values from -π to π, making it ideal for directional angle calculations.
Commonly used in geometry, graphics, robotics, and 2D movement logic.

Syntax


atan2(float $y, float $x): float
  • $y – Y-coordinate (opposite side)
  • $x – X-coordinate (adjacent side)
  • Returns – The angle in radians, between -π and π

File Name: atan2-example.php


<?php
echo atan2(1, 1);  // ➤ 0.78539816339745 (45 degrees, in radians)
echo "\n";
echo atan2(0, 1);  // ➤ 0 (along x-axis)
echo "\n";
echo atan2(1, 0);  // ➤ 1.5707963267949 (90 degrees, vertical)
?>

Convert to Degrees


$angle = atan2(1, 1);              // ➤ radians
$degrees = rad2deg($angle);        // ➤ 45 degrees
echo $degrees;

Use Cases

Use Case Description
Geometry Compute angle between two coordinates
Game development / AI Calculate direction of movement
Robotics Orientation of sensors and wheels
Physics Determine vector direction

Summary

Function Description
atan2() Returns arc tangent of y/x, with quadrant info
Input Two floats: y, x
Output Float (angle in radians, -π to π)