# PHP Tutorial - PHP Predefined Math Constants

## Definition

The following table lists the useful predefined math constants.

ConstantValueDescription
INFINFThe infinite
M_E2.7182818284590452354 e
M_EULER0.57721566490153286061 Euler constant
M_LNPI1.14472988584940017414 the natural logarithm of PI: log_e(pi)
M_LN20.69314718055994530942 the natural logarithm of 2: log_e 2
M_LN102.30258509299404568402 the natural logarithm of 10: log_e 10
M_LOG2E1.4426950408889634074 the base-2 logarithm of E: log_2 e
M_LOG10E0.43429448190325182765 the base-10 logarithm of E: log_10 e
M_PI3.14159265358979323846 Pi
M_PI_21.57079632679489661923 Pi/2
M_PI_40.78539816339744830962 Pi/4
M_1_PI0.31830988618379067154 1/Pi
M_2_PI0.63661977236758134308 2/Pi
M_SQRTPI1.77245385090551602729 the square root of PI: sqrt(pi)
M_2_SQRTPI1.12837916709551257390 2/square root of PI: 2/sqrt(pi)
M_SQRT1_20.70710678118654752440 the square root of 1/2: 1/sqrt(2)
M_SQRT21.41421356237309504880 the square root of 2: sqrt(2)
M_SQRT31.73205080756887729352 the square root of 3: sqrt(3)
NAN NANNot A Number
PHP_ROUND_HALF_UP1Round halves up
PHP_ROUND_HALF_DOWN2Round halves down
PHP_ROUND_HALF_EVEN3Round halves to even numbers
PHP_ROUND_HALF_ODD4Round halves to odd numbers