Numbers

Introduction

Numbers are at the heart of nearly every program — calculating totals, counting items, applying discounts, tracking scores. PHP has two main numeric types, integers and floats, and it is fairly relaxed about converting between numbers and numeric-looking strings.

This lesson looks at how PHP represents integers and floats, what happens when an integer grows too large, how PHP treats "numeric strings" in calculations, how to check whether a value is actually numeric, and how to format numbers nicely for display using number_format().

Integers vs Floats

An integer (int) is a whole number with no decimal point — positive, negative, or zero. A float (short for "floating-point number", also called double) is a number that can have a fractional/decimal part. PHP automatically decides which type a number literal is based on how it is written.

<?php
$quantity = 5;
$price = 19.99;
$negative = -12;
$zero = 0;

var_dump($quantity);
var_dump($price);

echo gettype($quantity) . "\n";
echo gettype($price) . "\n";
?>

int(5)
float(19.99)
integer
double

Dividing two integers can produce a float if the result is not a whole number — division in PHP always returns whatever type accurately represents the answer.

<?php
$a = 10 / 2;
$b = 10 / 3;

var_dump($a);
var_dump($b);
?>

int(5)
float(3.3333333333333)

Integer Overflow

PHP integers have a maximum size, exposed as the constant PHP_INT_MAX (on most modern 64-bit systems, this is 9,223,372,036,854,775,807). If a calculation produces a number larger than this, PHP does not throw an error — instead it automatically converts the result to a float, which can represent much larger (though less precise) values.

<?php
echo PHP_INT_MAX . "\n";

$max = PHP_INT_MAX;
$overflowed = $max + 1;

var_dump($overflowed);
?>

9223372036854775807
float(9.2233720368548E+18)

Numeric Strings in Arithmetic

A "numeric string" is a string whose content looks like a number, such as "42" or "3.14". PHP is happy to use numeric strings directly in arithmetic — it converts them to actual numbers on the fly.

<?php
$a = "10";
$b = "5";

$sum = $a + $b;
var_dump($sum);

$price = "19.99";
$quantity = "3";
echo ($price * $quantity) . "\n";
?>

int(15)
59.97

If a string is not fully numeric — for example, it contains letters mixed with digits — using it in arithmetic will either produce a warning/error (in modern PHP) or use only the leading numeric portion, depending on the PHP version. Non-numeric strings used in math should always be avoided.

<?php
$age = "25 years";

// In PHP 8+, this raises a warning because "25 years" is not a valid numeric string
$nextYearAge = (int) $age + 1;
echo $nextYearAge . "\n";
?>

26

Checking Numeric Types

PHP provides simple functions to check whether a value is a particular numeric type. is_int() (alias is_integer()) checks for a true integer, is_float() (alias is_double()) checks for a float, and is_numeric() checks whether a value — including a numeric string — could be treated as a number.

<?php
$a = 42;
$b = 3.14;
$c = "100";
$d = "hello";

var_dump(is_int($a));
var_dump(is_float($b));
var_dump(is_numeric($c));
var_dump(is_numeric($d));
var_dump(is_int($c));
?>

bool(true)
bool(true)
bool(true)
bool(false)
bool(false)

Notice that is_numeric("100") returns true (the string looks like a valid number), but is_int("100") returns false, because the value's actual type is a string, not an integer — is_int() checks the type, not just the appearance.

Formatting Numbers for Display

Raw numbers are great for calculations but often need reformatting before being shown to a user — adding thousands separators, rounding to a fixed number of decimal places, or displaying currency. number_format() handles all of this in one call.

<?php
$total = 1234567.891;

echo number_format($total) . "\n";
echo number_format($total, 2) . "\n";
echo number_format($total, 2, ",", ".") . "\n";

$price = 49.9;
echo "$" . number_format($price, 2) . "\n";
?>

1,234,568
1,234,567.89
1.234.567,89
$49.90

number_format() takes up to four arguments: the number itself, how many decimal places to show, the character used as the decimal point, and the character used as the thousands separator — which makes it easy to adapt to different regional number formats.

Common Mistakes

Best Practices

Frequently Asked Questions

Key Takeaways

Summary

Numbers in PHP are flexible: integers and floats convert into each other automatically, and even numeric strings can participate directly in calculations.

In this lesson, you learned the difference between integers and floats, what happens on overflow, how numeric strings behave in math, how to check numeric types, and how to format numbers for display. Next, you will explore PHP's built-in math functions in more depth.