JavaScript round to next 0.1

Question

I’m trying to round a number to the next highest 0.1 decimal point. For example if I have 2.51 I want it to be rounded up to 2.6, 3.91 to 4, 4.12 to 4.2 etc.

I’ve tried the following however this just rounds to nearest nearest 0.1 decimal and not the next 0.1

4.41.toFixed(1);

This rounds to 4.4 not 4.5 as intended

Possible duplicate of [How do you round to 1 decimal place in Javascript?](https://stackoverflow.com/questions/7342957/how-do-you-round-to-1-decimal-place-in-javascript) — Liam, Oct 09 '17 at 12:39
Multiply the number by then, use .ceil(), then divide by 10. — Dellirium, Oct 09 '17 at 12:40
Note that this is not mathematical correct as this should first be done when the secondary decimal is 5 or more. Ref: https://math.stackexchange.com/questions/3448/rules-for-rounding-positive-and-negative-numbers# — McMuffinDK, Oct 09 '17 at 12:55

alex · Answer 1 · 2017-10-09T12:43:15.080

4

Divide, ceil and then multiply and format.

(Math.ceil(num * 10) / 10).toFixed(1);

edited Oct 09 '17 at 12:43

answered Oct 09 '17 at 12:38

alex

479,566
201
878
984

score 1 · Answer 2 · answered Oct 09 '17 at 12:40

(Math.ceil(num * 10) / 10).toFixed(1);

would do it.

Note that this will still leave trailing digits on the 16th significant figure though due to the fact that floating point numbers cannot, in general, be truncated exactly to 1 decimal place. 4.5 works as it's a dyadic rational. The closest double to 2.6, for example, is 2.600000000000000088817841970012523233890533447265625.

score 0 · Answer 3 · answered Oct 09 '17 at 12:40

0

Just multiply the number with 10, use Math.ceil() and then divide it by 10.

Math.ceil(num * 10) / 10

answered Oct 09 '17 at 12:40

cyr_x

13,987
2
32
46

score 0 · Answer 4 · answered Oct 09 '17 at 12:41

0

Math.ceil(4.41*10)/10 // 4.5

More generally,

Math.ceil(x*10)/10

answered Oct 09 '17 at 12:41

falloutx

81
1
6

score 0 · Answer 5 · answered Oct 09 '17 at 12:52

You could add an offset of 0.049999999 and take the fixed value.

function round(v) {
    return (v + 0.049999999).toFixed(1);
}

console.log(round(2.51)); // 2.6
console.log(round(3.91)); // 4.0
console.log(round(4.12)); // 4.2
console.log(round(1));    // 4.2

JavaScript round to next 0.1

5 Answers5