I would like to know which width and height have my object with blur extended. When I have display mode - outline, I see only my object without blur. How can I see how large is blur? Is any possibility to see dimensions of this blur in outline?

I'm not familiar with the outline display mode. But since no one else has replied, I'll give it my best shot....which may not apply to this outline mode.

The only way I can think of is to slip a contrasting color behind the blurred object. Then using the Node tool cursor, point to the outer edge of the blur, and note the coordinates shown in the bottom right corner of the Inkscape window. Or draw another object around the blur, edit it to fit the blur, then look at the size in the Selector toolbar.

Sorry, I wish I could be more help. Maybe others will reply?

I think contrast color on background don´t help me. Because blur go to transparent color.

I dont believe theres any way to visualise the blurs in outline mode, although it sounds like a good idea. would be worth filing a feature request for if there isnt one already.

Thanks for your answer.