Definition and Usage

PHP Version
4+

The is_numeric() function checks whether a given value is a number or a numeric string.
It returns true if the value is numeric, and false otherwise.

Number
Refers to both the integer type, which contains whole numbers without decimal points, and the floating-point type, which includes numbers with decimal points.
Numeric String
In PHP, this includes strings that can be interpreted as integers or floating-point numbers, meaning any string that represents a numeric value.

Basic Example

PHP 
/* Integer Type */
var_dump(is_numeric(1));         // bool(true)
var_dump(is_numeric(0));         // bool(true)
var_dump(is_numeric(-10));       // bool(true)

/* Floating-Point Numbers (float) */
var_dump(is_numeric(1.0));       // bool(true)
var_dump(is_numeric(0.0));       // bool(true)
var_dump(is_numeric(3.14));      // bool(true)

/* Numeric Strings */
var_dump(is_numeric('1'));       // bool(true)
var_dump(is_numeric('0'));       // bool(true)
var_dump(is_numeric('10.5'));    // bool(true)
var_dump(is_numeric('123e2'));   // bool(true)

/* Non-Numeric Strings */
var_dump(is_numeric('hello'));    // bool(false)
var_dump(is_numeric('abc123'));   // bool(false)

/* Results of Numeric Operations */
var_dump(is_numeric(1 + 1));     // bool(true)
var_dump(is_numeric(10 / 2));    // bool(true)
var_dump(is_numeric(9 / 2));     // bool(true)

/* Type Casting */
var_dump(is_numeric((float) '1'));   // bool(true)
var_dump(is_numeric((int) '10.5'));  // bool(true)
var_dump(is_numeric((string) 123));  // bool(true)

Note:
The gettype() function returns the data type of the given value as a string.

Syntax

PHP 
is_numeric(mixed $value): bool

Parameters

Description of the is_numeric() function parameters
$value Required. The value to check whether it is a number or a numeric string.

Return Values

Returns true if the given value is a number or a numeric string, and false otherwise.

Changes as of PHP 8.0.0

  • Prior to PHP 8.0.0, numeric strings with trailing whitespace were not recognized as numbers by the is_numeric() function. For example, '35 ' would return false because it contained a trailing space.
  • Starting with PHP 8.0.0, is_numeric() now returns true for such strings.
Before PHP 8.0.0 
var_dump(is_numeric('35 ')); // bool(false) => numeric string with trailing whitespace
var_dump(is_numeric(' 35')); // bool(true)  => numeric string with leading whitespace
As of PHP 8.0.0 
var_dump(is_numeric('35 ')); // bool(true) => returns true starting from PHP 8.0.0
var_dump(is_numeric(' 35')); // bool(true) => still returns true for strings with leading whitespace

In short, this change allows is_numeric() to consider numeric strings with trailing whitespace as valid numbers, returning true.

Things to Keep in Mind

Strings that include a + or - sign are recognized as numbers by the is_numeric() function. For example, '+123' or '-456' are considered numeric.

PHP 
var_dump(is_numeric('+123')); // bool(true)
var_dump(is_numeric('-456')); // bool(true)

To check if a string contains only digits, use the ctype_digit() function.

PHP - Checking if a string contains only digits using ctype_digit() 
var_dump(ctype_digit('+123')); // bool(false)
var_dump(ctype_digit('-456')); // bool(false)

var_dump(ctype_digit('456'));  // bool(true)

Code Explanation
The ctype_digit() function checks whether a given string consists entirely of digits (0–9).
It returns true if all characters are digits, and false otherwise.

References

See also