The following table lists the useful predefined math constants.
| Constant | Value | Description |
|---|---|---|
| INF | INF | The infinite |
| M_E | 2.7182818284590452354 | e |
| M_EULER | 0.57721566490153286061 | Euler constant |
| M_LNPI | 1.14472988584940017414 | the natural logarithm of PI: log_e(pi) |
| M_LN2 | 0.69314718055994530942 | the natural logarithm of 2: log_e 2 |
| M_LN10 | 2.30258509299404568402 | the natural logarithm of 10: log_e 10 |
| M_LOG2E | 1.4426950408889634074 | the base-2 logarithm of E: log_2 e |
| M_LOG10E | 0.43429448190325182765 | the base-10 logarithm of E: log_10 e |
| M_PI | 3.14159265358979323846 | Pi |
| 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 | the square root of PI: sqrt(pi) |
| M_2_SQRTPI | 1.12837916709551257390 | 2/square root of PI: 2/sqrt(pi) |
| M_SQRT1_2 | 0.70710678118654752440 | the square root of 1/2: 1/sqrt(2) |
| M_SQRT2 | 1.41421356237309504880 | the square root of 2: sqrt(2) |
| M_SQRT3 | 1.73205080756887729352 | the square root of 3: sqrt(3) |
| NAN | NAN | Not A Number |
| PHP_ROUND_HALF_UP | 1 | Round halves up |
| PHP_ROUND_HALF_DOWN | 2 | Round halves down |
| PHP_ROUND_HALF_EVEN | 3 | Round halves to even numbers |
| PHP_ROUND_HALF_ODD | 4 | Round halves to odd numbers |