round

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

round — 对浮点数进行四舍五入

说明

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

返回将 val 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

val

要处理的值。

precision

可选的十进制小数点后数字的数目。

If the precision is positive, val is rounded to precision significant digits after the decimal point.

If the precision is negative, val is rounded to precision significant digits before the decimal point, i.e. to the nearest multiple of pow(10, -precision), e.g. for a precision of -1 val is rounded to tens, for a precision of -2 to hundreds, etc.

mode

Use one of the following constants to specify the mode in which rounding occurs.

常量 说明
PHP_ROUND_HALF_UP Rounds val away from zero when it is half way there, making 1.5 into 2 and -1.5 into -2.
PHP_ROUND_HALF_DOWN Rounds val towards zero when it is half way there, making 1.5 into 1 and -1.5 into -1.
PHP_ROUND_HALF_EVEN Rounds val towards the nearest even value when it is half way there, making both 1.5 and 2.5 into 2.
PHP_ROUND_HALF_ODD Rounds val towards the nearest odd value when it is half way there, making 1.5 into 1 and 2.5 into 3.

返回值

The value rounded to the given precision as a float.

范例

Example #1 round() 例子

<?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));
?>

以上例程会输出：

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

Example #2 How precision affects a 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));
?>

以上例程会输出：

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

Example #3 mode 例子

<?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));
?>

以上例程会输出：

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)

Example #4 mode with precision examples

<?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));
?>

以上例程会输出：

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

User Contributed Notes

Astro 27-Feb-2020 08:32
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.
Hayley Watson 05-Sep-2019 12:17
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.
goreyshi at gmail dot com 10-Jul-2018 09:34
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
Mojo urk 26-Jan-2018 07:28
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.
Anonymous 31-Aug-2017 02:23
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
armanhakimsagar at gmail dot com 06-Aug-2017 02:25
$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";
    }
depaula at unilogica dot com 13-Jan-2017 05:51
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
greghenle at gmail dot com 28-Nov-2016 09:25
/**
 * 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
 *
 */
Anonymous 17-Nov-2016 11:33
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
jongbumi at gmail dot com 12-May-2016 06:25
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
?>
php at persignum dot com 03-Aug-2015 07:30
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;
}
slimusgm at gmail dot com 02-Sep-2014 03:34
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)
serg at kalachev dot ru 24-Aug-2014 06:31
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
esion99 at gmail dot com 01-Jul-2014 10:49
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

?>
spectrumcat at gmail dot com 19-Mar-2014 02:22
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
takingsides at gmail dot com 07-Mar-2014 03:00
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);
}
?>
djcox99 at googlemail dot com 13-Jan-2014 11:28
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.
craft at ckdevelop dot org 17-Dec-2013 01:34
function mround($val, $f=2, $d=6){
    return sprintf("%".$d.".".$f."f", $val);
}

echo mround(34.89999);  //34.90
dastra 12-Jul-2012 11:16
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));
christian at deligant dot net 15-Sep-2011 01:24
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
?>
omnibus at omnibus dot edu dot pl 19-Nov-2010 02:26
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.
Anonymous 07-Oct-2010 04:07
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);
}
?>
feha at vision dot to 27-Aug-2010 07:59
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
lossantis at ig dot com dot br 15-Jul-2010 07:02
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]
Anonymous 02-Nov-2009 08:52
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;
    }
?>
michaeldnelson dot mdn at gmail dot com 25-Sep-2009 06:42
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
?>
Bevan 17-Sep-2009 12:24
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);
}
?>
martinr at maarja dot net 12-Jan-2008 03:40
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
maxteiber at gmail dot com 16-Oct-2006 05:15
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.
terry at scribendi dot com 12-Jan-2004 11:45
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'.
php at silisoftware dot com 14-Aug-2002 02:15
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;
}
?>
twan at ecreation dot nl 15-May-2000 06:51
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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