PHP 8.3.4 Released!

round

(PHP 4, PHP 5, PHP 7, PHP 8)

round对浮点数进行四舍五入

说明

round(int|float $num, int $precision = 0, int $mode = PHP_ROUND_HALF_UP): float

返回将 num 根据指定精度 precision(十进制小数点后数字的数目)进行四舍五入的结果。precision 也可以是负数或零(默认值)。

参数

num

要处理的值。

precision

可选的十进制小数点后数字的数目。

如果 precision 是正数,则 num 会四舍五入到小数点后 precision 位有效数字。

如果 precision 是负数,则 num 四舍五入到小数点前 precision 位有效数字。即 pow(10, -$precision) 最接近的倍数,例如,precision 为 -1,num 可以四舍五入到十位,precision 为 -2,num 可以四舍五入到百位,等等。

mode

使用以下常量指定四舍五入发生的模式。

常量 说明
PHP_ROUND_HALF_UP num 恰好处于中间时,将其向远离零的方向舍入,使 1.5 变为 2,-1.5 变为 -2。
PHP_ROUND_HALF_DOWN num 恰好处于中间时,将其向靠近零的方向舍入,使 1.5 变为 1,-1.5 变为 -1。
PHP_ROUND_HALF_EVEN num 四舍五入到最接近的偶数值,1.5 和 2.5 都变为 2。
PHP_ROUND_HALF_ODD num 四舍五入到最接近的奇数值,1.5 变为 1,2.5 变为 3。

返回值

值是四舍五入到指定 precision 精度的 float

更新日志

版本 说明
8.0.0 num 不再接受支持数字转换的内部对象。

示例

示例 #1 round() 示例

<?php
var_dump
(round(3.4));
var_dump(round(3.5));
var_dump(round(3.6));
var_dump(round(3.6, 0));
var_dump(round(5.045, 2));
var_dump(round(5.055, 2));
var_dump(round(345, -2));
var_dump(round(345, -3));
var_dump(round(678, -2));
var_dump(round(678, -3));
?>

以上示例会输出:

float(3)
float(4)
float(4)
float(4)
float(5.05)
float(5.06)
float(300)
float(0)
float(700)
float(1000)

示例 #2 precision 如何影响 float

<?php
$number
= 135.79;

var_dump(round($number, 3));
var_dump(round($number, 2));
var_dump(round($number, 1));
var_dump(round($number, 0));
var_dump(round($number, -1));
var_dump(round($number, -2));
var_dump(round($number, -3));
?>

以上示例会输出:

float(135.79)
float(135.79)
float(135.8)
float(136)
float(140)
float(100)
float(0)

示例 #3 mode 示例

<?php
echo 'Rounding modes with 9.5' . PHP_EOL;
var_dump(round(9.5, 0, PHP_ROUND_HALF_UP));
var_dump(round(9.5, 0, PHP_ROUND_HALF_DOWN));
var_dump(round(9.5, 0, PHP_ROUND_HALF_EVEN));
var_dump(round(9.5, 0, PHP_ROUND_HALF_ODD));

echo
PHP_EOL;
echo
'Rounding modes with 8.5' . PHP_EOL;
var_dump(round(8.5, 0, PHP_ROUND_HALF_UP));
var_dump(round(8.5, 0, PHP_ROUND_HALF_DOWN));
var_dump(round(8.5, 0, PHP_ROUND_HALF_EVEN));
var_dump(round(8.5, 0, PHP_ROUND_HALF_ODD));
?>

以上示例会输出:

Rounding modes with 9.5
float(10)
float(9)
float(10)
float(9)

Rounding modes with 8.5
float(9)
float(8)
float(8)
float(9)

示例 #4 带 precisionmode 示例

<?php
echo 'Using PHP_ROUND_HALF_UP with 1 decimal digit precision' . PHP_EOL;
var_dump(round( 1.55, 1, PHP_ROUND_HALF_UP));
var_dump(round(-1.55, 1, PHP_ROUND_HALF_UP));

echo
PHP_EOL;
echo
'Using PHP_ROUND_HALF_DOWN with 1 decimal digit precision' . PHP_EOL;
var_dump(round( 1.55, 1, PHP_ROUND_HALF_DOWN));
var_dump(round(-1.55, 1, PHP_ROUND_HALF_DOWN));

echo
PHP_EOL;
echo
'Using PHP_ROUND_HALF_EVEN with 1 decimal digit precision' . PHP_EOL;
var_dump(round( 1.55, 1, PHP_ROUND_HALF_EVEN));
var_dump(round(-1.55, 1, PHP_ROUND_HALF_EVEN));

echo
PHP_EOL;
echo
'Using PHP_ROUND_HALF_ODD with 1 decimal digit precision' . PHP_EOL;
var_dump(round( 1.55, 1, PHP_ROUND_HALF_ODD));
var_dump(round(-1.55, 1, PHP_ROUND_HALF_ODD));
?>

以上示例会输出:

Using PHP_ROUND_HALF_UP with 1 decimal digit precision
float(1.6)
float(-1.6)

Using PHP_ROUND_HALF_DOWN with 1 decimal digit precision
float(1.5)
float(-1.5)

Using PHP_ROUND_HALF_EVEN with 1 decimal digit precision
float(1.6)
float(-1.6)

Using PHP_ROUND_HALF_ODD with 1 decimal digit precision
float(1.5)
float(-1.5)

参见

add a note

User Contributed Notes 32 notes

up
316
takingsides at gmail dot com
10 years ago
In my opinion this function lacks two flags:

- PHP_ROUND_UP - Always round up.
- PHP_ROUND_DOWN - Always round down.

In accounting, it's often necessary to always round up, or down to a precision of thousandths.

<?php
function round_up($number, $precision = 2)
{
$fig = (int) str_pad('1', $precision, '0');
return (
ceil($number * $fig) / $fig);
}

function
round_down($number, $precision = 2)
{
$fig = (int) str_pad('1', $precision, '0');
return (
floor($number * $fig) / $fig);
}
?>
up
33
depaula at unilogica dot com
7 years ago
As PHP doesn't have a a native number truncate function, this is my solution - a function that can be usefull if you need truncate instead round a number.

<?php
/**
* Truncate a float number, example: <code>truncate(-1.49999, 2); // returns -1.49
* truncate(.49999, 3); // returns 0.499
* </code>
* @param float $val Float number to be truncate
* @param int f Number of precision
* @return float
*/
function truncate($val, $f="0")
{
if((
$p = strpos($val, '.')) !== false) {
$val = floatval(substr($val, 0, $p + 1 + $f));
}
return
$val;
}
?>

Originally posted in http://stackoverflow.com/a/12710283/1596489
up
2
Anonymous
7 years ago
Note that PHP 5.3 didn't just introduce $mode, it rewrote the rounding implementation completely to eliminate many kinds of rounding errors common to rounding floating point values.

That's why round() gives you the correct result even when floor/ceil don't.
For example, floor(0.285 * 100 + 0.5) VS round(0.285*100 + 0.5). First one gives 28, second one gives 29.

More details here: https://wiki.php.net/rfc/rounding
up
29
slimusgm at gmail dot com
9 years ago
If you have negative zero and you need return positive number simple add +0:

$number = -2.38419e-07;
var_dump(round($number,1));//float(-0)
var_dump(round($number,1) + 0);//float(0)
up
13
serg at kalachev dot ru
9 years ago
Excel-like ROUNDUP function:

public static function round_up($value, $places)
{
$mult = pow(10, abs($places));
return $places < 0 ?
ceil($value / $mult) * $mult :
ceil($value * $mult) / $mult;
}

echo round_up(12345.23, 1); // 12345.3
echo round_up(12345.23, 0); // 12346
echo round_up(12345.23, -1); // 12350
echo round_up(12345.23, -2); // 12400
echo round_up(12345.23, -3); // 13000
echo round_up(12345.23, -4); // 20000
up
7
Mojo urk
6 years ago
Solving round_down() problem:
-----------------------------
Use of <?php floor(pow(10, $precision) * $value) / pow(10, $precision); ?> fails in some cases, e.g. round_down(2.05, 2) gives incorrect 2.04.
Here is a "string" solution (https://stackoverflow.com/a/26491492/1245149) of the problem (a negative precision is not covered):

<?php
function round_down($value, $precision) {
$value = (float)$value;
$precision = (int)$precision;
if (
$precision < 0) {
$precision = 0;
}
$decPointPosition = strpos($value, '.');
if (
$decPointPosition === false) {
return
$value;
}
return (float)(
substr($value, 0, $decPointPosition + $precision + 1));
}
?>

Solving round_up() problem:
---------------------------
Use of <?php ceil(pow(10, $precision) * $value) / pow(10, $precision);?> fails in some cases, e.g. round_up(2.22, 2) gives incorrect 2.23 (https://stackoverflow.com/a/8239620/1245149).
Adapting the above round_down() "string" solution I have got this result (a negative precision is not covered):

<?php
function round_up($value, $precision) {
$value = (float)$value;
$precision = (int)$precision;
if (
$precision < 0) {
$precision = 0;
}
$decPointPosition = strpos($value, '.');
if (
$decPointPosition === false) {
return
$value;
}
$floorValue = (float)(substr($value, 0, $decPointPosition + $precision + 1));
$followingDecimals = (int)substr($value, $decPointPosition + $precision + 1);
if (
$followingDecimals) {
$ceilValue = $floorValue + pow(10, -$precision); // does this give always right result?
}
else {
$ceilValue = $floorValue;
}
return
$ceilValue;
}
?>

I don't know it is bulletproof, but at least it removes the above mentioned fail. I have done no binary-to-decimal-math-analysis but if `$floorValue + pow(10, 0 - $precision)` works
always as expected then it should be ok.
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21
djcox99 at googlemail dot com
10 years ago
I discovered that under some conditions you can get rounding errors with round when converting the number to a string afterwards.

To fix this I swapped round() for number_format().

Unfortunately i cant give an example (because the number cant be represented as a string !)

essentially I had round(0.688888889,2);

which would stay as 0.68888889 when printed as a string.

But using number_format it correctly became 0.69.
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10
craft at ckdevelop dot org
10 years ago
function mround($val, $f=2, $d=6){
return sprintf("%".$d.".".$f."f", $val);
}

echo mround(34.89999); //34.90
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11
jongbumi at gmail dot com
7 years ago
PHP 5.3, 5.4, 5.5
<?php
$fInfinty
= pow(1000, 1000); // float(INF)
$fResult = round(123.456, $fInfinty); // double(123)
?>

PHP 5.6
<?php
$fInfinty
= pow(1000, 1000); // float(INF)
$fResult = round(123.456, $fInfinty); // float(0)
?>

PHP 7
<?php
$fInfinty
= pow(1000, 1000); // float(INF)
$fResult = round(123.456, $fInfinty); // null
?>
up
18
esion99 at gmail dot com
9 years ago
Unexpected result or misunderstanding (php v5.5.9)

<?php

echo round(1.55, 1, PHP_ROUND_HALF_DOWN); // 1.5
echo round(1.551, 1, PHP_ROUND_HALF_DOWN); //1.6

?>
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10
christian at deligant dot net
12 years ago
this function (as all mathematical operators) takes care of the setlocale setting, resulting in some weirdness when using the result where the english math notation is expected, as the printout of the result in a width: style attribute!

<?php
$a
=3/4;
echo
round($a, 2); // 0.75

setlocale(LC_ALL, 'it_IT@euro', 'it_IT', 'it');
$b=3/4;
echo
round($b,2); // 0,75
?>
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19
twan at ecreation dot nl
23 years ago
If you'd only want to round for displaying variables (not for calculating on the rounded result) then you should use printf with the float:

<?php printf ("%6.2f",3.39532); ?>

This returns: 3.40 .
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17
Anonymous
13 years ago
Here is function that rounds to a specified increment, but always up. I had to use it for price adjustment that always went up to $5 increments.

<?php
function roundUpTo($number, $increments) {
$increments = 1 / $increments;
return (
ceil($number * $increments) / $increments);
}
?>
up
8
michaeldnelson dot mdn at gmail dot com
14 years ago
This function will let you round to an arbitrary non-zero number. Zero of course causes a division by zero.

<?php
function roundTo($number, $to){
return
round($number/$to, 0)* $to;
}

echo
roundTo(87.23, 20); //80
echo roundTo(-87.23, 20); //-80
echo roundTo(87.23, .25); //87.25
echo roundTo(.23, .25); //.25
?>
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4
greghenle at gmail dot com
7 years ago
/**
* Round to first significant digit
* +N to +infinity
* -N to -infinity
*
*/
function round1stSignificant ( $N ) {
if ( $N === 0 ) {
return 0;
}

$x = floor ( log10 ( abs( $N ) ) );

return ( $N > 0 )
? ceil( $N * pow ( 10, $x * -1 ) ) * pow( 10, $x )
: floor( $N * pow ( 10, $x * -1 ) ) * pow( 10, $x );
}

echo round1stSignificant( 39144818 ) . PHP_EOL;
echo round1stSignificant( 124818 ) . PHP_EOL;
echo round1stSignificant( 0.07468 ) . PHP_EOL;
echo round1stSignificant( 0 ) . PHP_EOL;
echo round1stSignificant( -0.07468 ) . PHP_EOL;

/**
* Output
*
* 40000000
* 200000
* 0.08
* 0
* -0.08
*
*/
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9
martinr at maarja dot net
16 years ago
Please note that the format of this functions output also depends on your locale settings. For example, if you have set your locale to some country that uses commas to separate decimal places, the output of this function also uses commas instead of dots.

This might be a problem when you are feeding the rounded float number into a database, which requires you to separate decimal places with dots.

See it in action:
<?php
echo round('3.5558', 2);
setlocale(constant('LC_ALL'), 'et_EE.UTF-8');
echo
'<br />'. round('3.5558', 2);
?>

The output will be:
3.56
3,56
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4
dastra
11 years ago
round() will sometimes return E notation when rounding a float when the amount is small enough - see https://bugs.php.net/bug.php?id=44223 . Apparently it's a feature.

To work around this "feature" when converting to a string, surround your round statement with an sprintf:

sprintf("%.10f", round( $amountToBeRounded, 10));
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9
php at silisoftware dot com
21 years ago
Here's a function to round to an arbitary number of significant digits. Don't confuse it with rounding to a negative precision - that counts back from the decimal point, this function counts forward from the Most Significant Digit.

ex:

<?php
round
(1241757, -3); // 1242000
RoundSigDigs(1241757, 3); // 1240000
?>

Works on negative numbers too. $sigdigs should be >= 0

<?php
function RoundSigDigs($number, $sigdigs) {
$multiplier = 1;
while (
$number < 0.1) {
$number *= 10;
$multiplier /= 10;
}
while (
$number >= 1) {
$number /= 10;
$multiplier *= 10;
}
return
round($number, $sigdigs) * $multiplier;
}
?>
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2
goreyshi at gmail dot com
5 years ago
When you have a deal with money like dollars, you need to display it under this condition:
-format all number with two digit decimal for cents.
-divide 1000 by ,
-round half down for number with more than two decimal

I approach it using round function inside the number_format function:

number_format((float)round( 625.371 ,2, PHP_ROUND_HALF_DOWN),2,'.',',') // 625.37
number_format((float)round( 625.379 ,2, PHP_ROUND_HALF_DOWN),2,'.',',') // 625.38
number_format((float)round( 1211.20 ,2, PHP_ROUND_HALF_DOWN),2,'.',',') // 1,211.20
number_format((float)round( 625 ,2, PHP_ROUND_HALF_DOWN),2,'.',',') // 625.00
up
0
Hayley Watson
4 years ago
It should just be noted that what is called "precision" on this page is more correctly called accuracy; precision is the total number of significant digits on both sides of the decimal point, while accuracy is the number of digits to the right of the point. It's a common confusion.
up
1
feha at vision dot to
13 years ago
Here is a short neat function to round minutes (hour) ...

<?php

function minutes_round ($hour = '14:03:32', $minutes = '5', $format = "H:i")
{
// by Femi Hasani [www.vision.to]
$seconds = strtotime($hour);
$rounded = round($seconds / ($minutes * 60)) * ($minutes * 60);
return
date($format, $rounded);
}

?>

You decide to round to nearest minute ...
example will produce : 14:05
up
-2
omnibus at omnibus dot edu dot pl
13 years ago
Beware strange behaviour if number is negative and precision is bigger than the actual number of digits after comma.

round(-0.07, 4);

returns

-0.07000000000000001

So if you validate it against a regular expression requiring the maximum amount of digits after comma, you'll get into trouble.
up
-1
Astro
4 years ago
Okay, final version of my function:

function NumberPrecision($n, $precision=0, $is_round=true)
{
if ($is_round)
{
$r = 5 * pow(10, -($precision+1));
$n += (($n < 0) ? -$r : $r);
}

$comma = '.';

$r = 5 * pow(10, -($precision+2));
$n += (($n > 0) ? -$r : $r);
$n = number_format($n, $precision+1, $comma, '');

$n .= $comma;
list($n, $frac) = explode($comma, $n, 2);
$n = rtrim(rtrim($n, $comma) . $comma . substr($frac, 0, $precision), $comma);
return ($n);
}

It can be useful in come cases when built-in function like round() or number_format() returns unexpected results. Works with positive and negative numbers, zero, numbers like 1/12, 0.3, numbers in scientific notation etc.
up
-1
terry at scribendi dot com
20 years ago
To round any number to a given number of significant digits, use log10 to find out its magnitude:

<?php round($n, ceil(0 - log10($n)) + $sigdigits); ?>

Or when you have to display a per-unit price which may work out to be less than a few cents/pence/yen you can use:

<?php
// $exp = currency decimal places - 0 for Yen/Won, 2 for most others
$dp = ceil(0 - log10($n)) + $sigdigits;
$display = number_format($amount, ($exp>$dp)?$exp:$dp);
?>

This always displays at least the number of decimal places required by the currency, but more if displaying the unit price with precision requires it - eg: 'English proofreading from $0.0068 per word', 'English beer from $6.80 per pint'.
up
-2
Anonymous
14 years ago
This functions return ceil($nb) if the double or float value is bigger than "$nb.5" else it's return floor($nb)

<?php
function arounds_int($nb) {

if(!
is_numeric($nb)) {
return
false;
}

$sup = round($nb);
$inf = floor($nb);
$try = (double) $inf . '.5' ;

if(
$nb > $try) {
return
$sup;
}

return
$inf;
}
?>
up
-3
spectrumcat at gmail dot com
9 years ago
In case someone will need a "graceful" rounding (that changes it's precision to get a non 0 value) here's a simple function:

function gracefulRound($val, $min = 2, $max = 4) {
$result = round($val, $min);
if ($result == 0 && $min < $max) {
return gracefulRound($val, ++$min, $max);
} else {
return $result;
}
}

Usage:
$_ = array(0.5, 0.023, 0.008, 0.0007, 0.000079, 0.0000048);
foreach ($_ as $val) {
echo "{$val}: ".gracefulRound($val)."\n";
}

Output:
0.5: 0.5
0.023: 0.02
0.008: 0.01
0.0007: 0.001
0.000079: 0.0001
0.0000048: 0
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-4
maxteiber at gmail dot com
17 years ago
the result of this function always depends on the underlying C function. There have been a lot of compiler bugs and floating-point precission problems involving this function. Right now the following code:

<?php
echo round(141.075, 2);
?>

returns:

141.07

on my machine.
So never really trust this function when you do critical calculations like accounting stuff!
Instead: use only integers or use string comparisons.
up
-4
Anonymous
6 years ago
This function has strange. behaviors:

<?php
echo round(0.045, 2); // 0.05
echo round(0.45, 1); // 0.5
echo round(1.045-1, 2); // 0.04 !!!
echo round(1.45-1, 1); // 0.5
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-7
lossantis at ig dot com dot br
13 years ago
Since the mode parameter for options like PHP_ROUND_HALF_UP is available as of PHP 5.3, here is an alternative for ceiling:

<?php echo 252 / 40; // 6.3 ?>

If I round this:

<?php echo round(252 / 40); // 6 ?>

You can also use a ceil (which might be useful for pagination):

<?php echo ceil(252/40); // 7 ?>

[Edited by: googleguy@php.net for clarity]
up
-5
php at persignum dot com
8 years ago
Because this function is missing round up and round down constants and the top note doesn't really show you how to round up or down to the nearest number, here is an easy way to always round up or always round down to the nearest number.

int is the number you want to round

n is the nearest number you want rounded to.

Round up to the nearest number

function round_up($int, $n) {
return ceil($int / $n) * $n;
}

And to round down to the nearest number

function round_down(int, $n) {
return floor($int / $n) * $n;
}
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-11
Bevan
14 years ago
Formats a number to the specified number of significant figures.

<?php
/**
* Formats numbers to the specified number of significant figures.
*
* @author Bevan Rudge, Drupal.geek.nz
*
* @param number $number
* The number to format.
* @param integer $sf
* The number of significant figures to round and format the number to.
* @return string
* The rounded and formatted number.
*/
function format_number_significant_figures($number, $sf) {
// How many decimal places do we round and format to?
// @note May be negative.
$dp = floor($sf - log10(abs($number)));
// Round as a regular number.
$number = round($number, $dp);
// Leave the formatting to format_number(), but always format 0 to 0dp.
return number_format($number, 0 == $number ? 0 : $dp);
}
?>
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-10
armanhakimsagar at gmail dot com
6 years ago
$a = .9;

$b = .8;

$d = .1;

$e = .2;

$x = $a-$b;

$y = $e-$d;

$f = round($x,2);

echo $f;

if($f==$y){

echo "ok";
}
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