The constants below are always available as part of the PHP core.
Math constants
Constant
Value
Description
M_PI
3.14159265358979323846
Pi
M_E
2.7182818284590452354
e
M_LOG2E
1.4426950408889634074
log_2 e
M_LOG10E
0.43429448190325182765
log_10 e
M_LN2
0.69314718055994530942
log_e 2
M_LN10
2.30258509299404568402
log_e 10
M_PI_2
1.57079632679489661923
pi/2
M_PI_4
0.78539816339744830962
pi/4
M_1_PI
0.31830988618379067154
1/pi
M_2_PI
0.63661977236758134308
2/pi
M_SQRTPI
1.77245385090551602729
sqrt(pi) [5.2.0]
M_2_SQRTPI
1.12837916709551257390
2/sqrt(pi)
M_SQRT2
1.41421356237309504880
sqrt(2)
M_SQRT3
1.73205080756887729352
sqrt(3) [5.2.0]
M_SQRT1_2
0.70710678118654752440
1/sqrt(2)
M_LNPI
1.14472988584940017414
log_e(pi) [5.2.0]
M_EULER
0.57721566490153286061
Euler constant [5.2.0]
Only M_PI is available in PHP versions up to and including PHP 4.0.0.
All other constants are available starting with PHP 4.0.0. Constants
labeled [5.2.0] were added in PHP 5.2.0.
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