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Table of Contents
Basic usage: only one parameter is passed
Control the number of decimal places: the second parameter precision
Different rounding methods: the third parameter mode
Note: Floating point accuracy issues
Home Backend Development PHP Tutorial How to use php round function?

How to use php round function?

Jul 02, 2025 pm 05:25 PM

PHP's round() function is used to round floating point numbers. The basic usage is to pass in a floating point number, and the integer is rounded by rounding by default; 1. The reserved decimal places can be controlled through the second parameter precision, such as round(3.14159, 2) output 3.14; 2. When precision is negative, carry to the left, such as round(1234.56, -2) output 1200; 3. The third parameter mode can specify the rounding method, and the default PHP_ROUND_HALF_UP is rounded, and PHP_ROUND_HALF_DOWN does not carry. 5; in addition, it is necessary to note that floating point accuracy issues may lead to unexpected results. It is recommended to use them in combination with number_format() or bcmath extension to ensure accuracy.

How to use php round function?

PHP's round() function is used to round floating point numbers. It is not complicated to use, but there are several details that are easily overlooked. Here are a few usages and precautions you can really use.

How to use php round function?

Basic usage: only one parameter is passed

The easiest way to use it is to just pass a floating point number in:

How to use php round function?
 echo round(3.4); // Output 3
echo round(3.6); // Output 4

In this case, the rounding rule will be processed by default, and the integer part will be retained.


Control the number of decimal places: the second parameter precision

You can control how many decimal places to retain by the second parameter:

How to use php round function?
 echo round(3.14159, 2); // Output 3.14
echo round(2.71828, 3); // Output 2.718
  • The second parameter can be a negative number, which will "carry" to the left, for example:
     echo round(1234.56, -2); // Output 1200

    At this time, the hundred people are rounded.


Different rounding methods: the third parameter mode

round() also supports specifying rounding mode, which has an impact when processing certain specific values. There are two common patterns:

  • PHP_ROUND_HALF_UP (default): is the rounding we are familiar with.
  • PHP_ROUND_HALF_DOWN : No upward carriage when encountering .5.

For example:

 echo round(1.5, 0, PHP_ROUND_HALF_UP); // Output 2
echo round(1.5, 0, PHP_ROUND_HALF_DOWN); // Output 1

This function may come in handy when dealing with financial, statistical and other scenarios.


Note: Floating point accuracy issues

Sometimes you will find strange results, such as:

 echo round(0.58, 1); // It may output 0.6, or may not?

This is because there is a problem of accuracy loss when floating point numbers themselves are stored in computers. If you need more precise decimal operations, it is recommended to combine number_format() or use bcmath extension.


Basically that's it. By mastering these usages, you can deal with most scenarios that require rounding.

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