I'm currently using the build from Dec 28th, can confirm this issue. I thought it was something I was doing wrong, made a post about it on blenderartists;

Blender Artists Post

Picking the end of the ruler and dragging it off the screen does delete it, as someone in the thread suggested, this however isn't consistent with the manual. One or the other could use an update.

Hello.

Still not chance to delete the ruler -

Blender 2.8 2019-01-04 21:18 a77b63c56943

win 7 64bit: gforce nvidia gt 730

Regards

Sorry for trouble I have found resolution very fast.

On menu Annotations (under N key) there shows 'Ruler" Layer.

Only enough is to click on minus button and go out from Measure option.

When you come back, you can see so there is there is nothing left.

:)

Regards

I agree that this is very confusing. I would not expect to have to go to the Annotations panel to remove rulers + there are probably some updates missing.
Is this really how it should work, @William Reynish (billreynish) ?

I think we can make this a lot easier. In the top bar, we could have an enum with options to add, remove or move rulers.

i had the same problem, i solve it dragging the ruler out of the window.
I hope that it would be useful to someone :)

This problem seems to occur again with the most new releases. I can't remove the rulers dragging them out of the window, as I done before. The ruler stays in the viewport, even deleting it. It comes back.

The problem persists. I delete the ruler pressing X and, after a moment its comes back. Deleting and saving the file, and then reopening, the ruler comes back, too. And the ruler was not created by me.

Maybe it is fixed now. To turn off a measure, left click on the measure end point to select it, then x to delete it. I'm using Blender 2.9.1.0