Predefined Constants

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

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).

NAN (float): Not A Number
INF (float): Infinity

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

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User Contributed Notes 4 notes

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md2perpe at gmail dot com ¶

9 years ago

I just learnt of INF today and found out that it can be used in comparisons:

    echo 5000 < INF ? 'yes' : 'no';       // outputs 'yes'
    echo INF < INF ? 'yes' : 'no';        // outputs 'no'
    echo INF <= INF ? 'yes' : 'no';       // outputs 'yes'
    echo INF == INF ? 'yes' : 'no';       // outputs 'yes'

You can also take its negative:

    echo -INF < -5000 ? 'yes' : 'no';    // outputs 'yes'

Division by INF is allowed:

    echo 1/INF;    // outputs '0'

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Hayley Watson ¶

12 years ago

There are also the predefined PHP_INT_MAX and PHP_INT_SIZE constants, that describe the range of possible integer values.

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pemapmodder1970 at gmail dot com ¶

8 years ago

Although INF can be used for comparison against normal numbers and as a directed number, and behaves as reciprocal of zero, it is not like limit INF tends to infinity. These operations do not work:

<?php
var_dump(INF / INF); // float(NAN)
var_dump(INF - INF); // float(NAN)
?>

However, it works with arc-tangent:
<?php
var_dump(atan(INF) / M_PI); // float(0.5)
var_dump(atan2(INF, INF) / M_PI); // float(0.25)
var_dump(atan2(1, INF) / M_PI); // float(0)
?>

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Hayley Watson ¶

7 years ago

From PHP 7.2.0, the PHP_FLOAT_* constants are provided to describe the properties of floating point numbers that can be stored; PHP_FLOAT_MAX, for example, is analogous to PHP_INT_MAX and represents the largest possible floating-point number.

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