# Predefined Constants

The constants below are always available as part of the PHP core.

Mathematical Constants
`M_PI` (float)
  Approximation of the number π (pi). (`3.14159265358979323846`).
`M_E` (float)
  Approximation of Euler's number `e` (`2.7182818284590452354`).
`M_LOG2E` (float)
  Approximation of `log2(e)` (`1.4426950408889634074`).
`M_LOG10E` (float)
  Approximation of `log10(e)` (`0.43429448190325182765`).
`M_LN2` (float)
  Approximation of `ln(2)` (`0.69314718055994530942`).
`M_LN10` (float)
  Approximation of `ln(10)` (`2.30258509299404568402`).
`M_PI_2` (float)
  Approximation of `π/2` (`1.57079632679489661923`).
`M_PI_4` (float)
  Approximation of `π/4` (`0.78539816339744830962`).
`M_1_PI` (float)
  Approximation of `1/π` (`0.31830988618379067154`).
`M_2_PI` (float)
  Approximation of `2/π` (`0.63661977236758134308`).
`M_SQRTPI` (float)
  Approximation of `sqrt(π)` (`1.77245385090551602729`).
`M_2_SQRTPI` (float)
  Approximation of `2/sqrt(π)` (`1.12837916709551257390`).
`M_SQRT2` (float)
  Approximation of `sqrt(2)` (`1.41421356237309504880`).
`M_SQRT3` (float)
  Approximation of `sqrt(3)` (`1.73205080756887729352`).
`M_SQRT1_2` (float)
  Approximation of `1/sqrt(2)` (`0.70710678118654752440`).
`M_LNPI` (float)
  Approximation of `ln(π)` (`1.14472988584940017414`).
`M_EULER` (float)
  Approximation of Euler's constant γ (`0.57721566490153286061`).

IEEE 754 floating point constants
`NAN` (float)
  Not A Number
`INF` (float)
  Infinity

Rounding constants

> Note: As of PHP 8.4.0, it is recommended to use the RoundingMode enum instead.

`PHP_ROUND_HALF_UP` (int)
  Rounding half away from zero.
`PHP_ROUND_HALF_DOWN` (int)
  Rounding half toward zero.
`PHP_ROUND_HALF_EVEN` (int)
  Round halves to even numbers
`PHP_ROUND_HALF_ODD` (int)
  Round halves to odd numbers

`↑` and `↓` to navigate • `Enter` to select • `Esc` to close • `/` to open