I'm working with the last gimp version 2.10. I need to make circle selection with the ellipse tool, I need the circle selection to be with defined diameter size (for example 20 mm) What steps I should take to achieve the result?

First of all, Gimp is a raster (bitmap) editor and works in **pixels** although it can show equivalents as long as you realise these are tied to the printing resolution. An example is the standard template for A5(300ppi) which is set up in mm. see screenshot.

..but it can be any-old canvas size/resolution.

To make a circular selection of a given size (in millimetres)

You can set a fixed size but that is in pixels so the most direct way is see: screenshot

1. In the elliptical select tool options set the size units to mm from the drop down menu.

2. Draw any selection in the canvas.

3. Manually enter the size in the two height / width of selection boxes.

4. Click and drag the selection to the required position

5. Hit enter to fix the selection

rich: www.gimp-forum.net

Thank you very much , Does the 20 mm in the screenshot does it mean 20 mm size of the vertical and horizontal diameter of the circle?

Yes, but real world units only come into play when printed at the resolution specified. Are you going to print something? Set up the canvas first.

Remember Gimp works in pixels (gets calculator out)

You can have 20 mm @ 300 ppi (a print resolution) which gives 236 pixels

or 20 mm @ 72 ppi (typical screen resolution) = 57 pixels.

A common beginners mistake is not checking the resolution when making a new canvas.

Thanks I created the circles - and now I have other question -I want to distribute them evenly-with the same space between then.I chose the align tool and shift+click on all the circles. I clicked on distribute evenly in the horizontal-but it distribute the circles with even space - As you can see on the picture attached. What can be done to distribute with even space?

You want even spaces between the circles.

From your image, using the Gimp align tool, the centers are evenly spaced. Could do it by hand but using a plugin.

1. You need each circle on its own layer, and each layer autocropped to minimum size.

2. The plugin arrange-layers-0.2.py comes from

http://sourceforge.net/projects/gimp-tools/files/scripts/ down the page look for the date 2012-11-30

3. Find it bottom of the image menu Image -> Arrange layers -> Space -> Horizontally see screenshot

4. You will probably need to move back into position, link layers and use the move tools. see: screenshot

rich: www.gimp-forum.net