Rounding float/decimal to 3 decimal places exactly?

Question

I know there are many questions asking for this, but I have tried quite a few of the solutions but none seem to work exactly how I need it!

Most solutions work, however in my test data I have the float: 0.08095238095238096

If I round this to 4 I seem to get; 0.081 when I need to have 0.0809 and not rounded up that last place.

Also am I best using float or double for this type of number?

Thanks

Solution

You appear to want to round down to FOUR decimal places instead of rounding half up.

double d = 0.08095238095238096;
d = (long) (d * 10000) / 10000.0;

or

d = Math.floor(d * 10000) / 10000.0;

I assume you mean you want d = 0.0809 instead of 0.809.

Perhaps you are thinking of 3 significant digits which is a harder problem.

Its best to use double or BigDecimal instead of float unless you have a very good reason.

BTW: It is useful to have a clear idea of what you want, otherwise its going to be much harder to find it. ;)

Comments

[Bohemian]

Your problem is your original number is wrong. If you need to get 0.809 you'll need to start with 0.8095238095238096 (not 0.08095238095238096 as you have).

[tchrist]

possible duplicate of Round a double to 2 significant figures after decimal point