# How do you round to 1 decimal place in Javascript?

Can you round a number in javascript to 1 character after the decimal point (properly rounded)?

I tried the *10, round, /10 but it leaves two decimals at the end of the int.

`Math.round(num * 10) / 10` works, here is an example...

``````var number = 12.3456789
var rounded = Math.round(number * 10) / 10
// rounded is 12.3
``````

if you want it to have one decimal place, even when that would be a 0, then add...

``````var fixed = rounded.toFixed(1)
// fixed is always to 1 d.p.
// NOTE: .toFixed() returns a string!

// To convert back to number format
parseFloat(number.toFixed(2))
// 12.34
// but that will not retain any trailing zeros

// So, just make sure it is the last step before output,
// and use a number format during calculations!
``````

### EDIT: Add round with precision function...

Using this principle, for reference, here is a handy little round function that takes precision...

``````function round(value, precision) {
var multiplier = Math.pow(10, precision || 0);
return Math.round(value * multiplier) / multiplier;
}
``````

... usage ...

``````round(12345.6789, 2) // 12345.68
round(12345.6789, 1) // 12345.7
``````

... defaults to round to nearest whole number (precision 0) ...

``````round(12345.6789) // 12346
``````

... and can be used to round to nearest 10 or 100 etc...

``````round(12345.6789, -1) // 12350
round(12345.6789, -2) // 12300
``````

... and correct handling of negative numbers ...

``````round(-123.45, 1) // -123.4
round(123.45, 1) // 123.5
``````

... and can be combined with toFixed to format consistently as string ...

``````round(456.7, 2).toFixed(2) // "456.70"
``````
``````var number = 123.456;

console.log(number.toFixed(1)); // should round to 123.5
``````

If you use `Math.round(5.01)` you will get `5` instead of `5.0`.

If you use `toFixed` you run into rounding issues.

If you want the best of both worlds combine the two:

``````(Math.round(5.01 * 10) / 10).toFixed(1)
``````

You might want to create a function for this:

``````function roundedToFixed(_float, _digits){
var rounded = Math.pow(10, _digits);
return (Math.round(_float * rounded) / rounded).toFixed(_digits);
}
``````

`lodash` has a `round` method:

``````_.round(4.006);
// => 4

_.round(4.006, 2);
// => 4.01

_.round(4060, -2);
// => 4100
``````

Docs.

I vote for `toFixed()`, but, for the record, here's another way that uses bit shifting to cast the number to an int. So, it always rounds towards zero (down for positive numbers, up for negatives).

``````var rounded = ((num * 10) << 0) * 0.1;
``````

But hey, since there are no function calls, it's wicked fast. :)

And here's one that uses string matching:

``````var rounded = (num + '').replace(/(^.*?\d+)(\.\d)?.*/, '\$1\$2');
``````

I don't recommend using the string variant, just sayin.

Try with this:

``````var original=28.453

// 1.- round "original" to two decimals
var result = Math.round (original * 100) / 100  //returns 28.45

// 2.- round "original" to 1 decimal
var result = Math.round (original * 10) / 10  //returns 28.5

// 3.- round 8.111111 to 3 decimals
var result = Math.round (8.111111 * 1000) / 1000  //returns 8.111
``````

less complicated and easier to implement...

with this, you can create a function to do:

``````function RoundAndFix (n, d) {
var m = Math.pow (10, d);
return Math.round (n * m) / m;
}
``````

``````function RoundAndFix (n, d) {
var m = Math.pow (10, d);
return Math.round (n * m) / m;
}
console.log (RoundAndFix(8.111111, 3));``````

x = number, n = decimal-places:

``````function round(x, n) {
return Math.round(x * Math.pow(10, n)) / Math.pow(10, n)
}
``````
``````var num = 34.7654;

num = Math.round(num * 10) / 10;

console.log(num); // Logs: 34.8
``````

``````var round = function ( number, precision )
{
precision = precision || 0;
return parseFloat( parseFloat( number ).toFixed( precision ) );
}
``````

The input parameter number may "not" always be a number, in this case .toFixed does not exist.

ES 6 Version of Accepted Answer:

``````function round(value, precision) {
const multiplier = 10 ** (precision || 0);
return Math.round(value * multiplier) / multiplier;
}
``````

Why not just

``````let myNumber = 213.27321;
+myNumber.toFixed(1); // => 213.3
``````
1. toFixed: returns a string representing the given number using fixed-point notation.
2. Unary plus (+): The unary plus operator precedes its operand and evaluates to its operand but attempts to convert it into a number, if it isn't already.

However,you could accomplish the rounding off task as:

``````var value = Math.round(234.567*100)/100
``````

Will give you 234.56

Similarly

`````` var value = Math.round(234.567*10)/10
``````

Will give 234.5

In this way you can use a variable in the place of the constant as used above.

Using toPrecision method:

``````var a = 1.2345
a.toPrecision(2)

// result "1.2"
``````

Little Angular filter if anyone wants it:

``````angular.module('filters').filter('decimalPlace', function() {
return function(num, precision) {
var multiplier = Math.pow(10, precision || 0);
return Math.round(num * multiplier) / multiplier;
};
});
``````

use if via:

``````{{model.value| decimalPlace}}
{{model.value| decimalPlace:1}}
{{model.value| decimalPlace:2}}
``````

:)

In general, rounding is done by scaling: `round(num / p) * p`

Using the exponential notation handles rounding of +ve numbers, correctly. However, this method fails to round -ve edge cases correctly.

``````function round(num, precision = 2) {
var scaled = Math.round(num + "e" + precision);
return Number(scaled + "e" + -precision);
}

// testing some edge cases
console.log( round(1.005, 2) );  // 1.01 correct
console.log( round(2.175, 2) );  // 2.18 correct
console.log( round(5.015, 2) );  // 5.02 correct

console.log( round(-1.005, 2) );  // -1    wrong
console.log( round(-2.175, 2) );  // -2.17 wrong
console.log( round(-5.015, 2) );  // -5.01 wrong``````

Here, also is one function I wrote to do arithmetic rounding, you can test it yourself.

``````/**
* MidpointRounding away from zero ('arithmetic' rounding)
* Uses a half-epsilon for correction. (This offsets IEEE-754
* half-to-even rounding that was applied at the edge cases).
*/

function RoundCorrect(num, precision = 2) {
// half epsilon to correct edge cases.
var c = 0.5 * Number.EPSILON * num;
//	var p = Math.pow(10, precision); //slow
var p = 1; while (precision--> 0) p *= 10;
if (num < 0)
p *= -1;
return Math.round((num + c) * p) / p;
}

// testing some edge cases
console.log(RoundCorrect(1.005, 2));  // 1.01 correct
console.log(RoundCorrect(2.175, 2));  // 2.18 correct
console.log(RoundCorrect(5.015, 2));  // 5.02 correct

console.log(RoundCorrect(-1.005, 2));  // -1.01 correct
console.log(RoundCorrect(-2.175, 2));  // -2.18 correct
console.log(RoundCorrect(-5.015, 2));  // -5.02 correct``````

This seems to work reliably across anything I throw at it:

``````function round(val, multiplesOf) {
var s = 1 / multiplesOf;
var res = Math.ceil(val*s)/s;
res = res < val ? res + multiplesOf: res;
var afterZero = multiplesOf.toString().split(".")[1];
return parseFloat(res.toFixed(afterZero ? afterZero.length : 0));
}
``````

It rounds up, so you may need to modify it according to use case. This should work:

``````console.log(round(10.01, 1)); //outputs 11
console.log(round(10.01, 0.1)); //outputs 10.1
``````

If you care about proper rounding up then:

``````function roundNumericStrings(str , numOfDecPlacesRequired){
var roundFactor = Math.pow(10, numOfDecPlacesRequired);
return (Math.round(parseFloat(str)*roundFactor)/roundFactor).toString();  }
``````

Else if you don't then you already have a reply from previous posts

``````str.slice(0, -1)
``````

`Math.round( num * 10) / 10` doesn't work.

For example, `1455581777.8-145558160.4` gives you `1310023617.3999999`.

So only use `num.toFixed(1)`

I made one that returns number type and also places decimals only if are needed (no 0 padding).

Examples:

``````roundWithMaxPrecision(11.234, 2); //11.23
roundWithMaxPrecision(11.234, 1); //11.2
roundWithMaxPrecision(11.234, 4); //11.23
roundWithMaxPrecision(11.234, -1); //10

roundWithMaxPrecision(4.2, 2); //4.2
roundWithMaxPrecision(4.88, 1); //4.9
``````

The code:

``````function roundWithMaxPrecision (n, precision) {
return Math.round(n * Math.pow(10, precision)) / Math.pow(10, precision);
}
``````

I found a way to avoid the precision problems:

``````function badRound (num, precision) {
const x = 10 ** precision;
return Math.round(num * x) / x
}

function round (num, precision) {
const x = 10 ** (precision + 1);
const y = 10 ** precision;
return Math.round(Math.round(num * x) / 10) / y
}
// round(1.005, 2) --> 1.01
``````
``````Math.round( mul/count * 10 ) / 10

Math.round(Math.sqrt(sqD/y) * 10 ) / 10
``````

Thanks

``````function rnd(v,n=2) {
return Math.round((v+Number.EPSILON)*Math.pow(10,n))/Math.pow(10,n)
}
``````

this one catch the corner cases well