Use the transform panel to determine the exact with and height of your outer margins.
Indesign margin and gutter.
Select format document margins and assign margins that include the additional bleed example.
Assuming i guessed correctly are you trying to define the gutter width or gutter position.
To adjust column guides manually drag them horizontally to new positions producing unequal widths.
210x297 less 10mm each side would be 190x277.
To achieve uniform spacing set your gutters to the same value as or a multiple of 1 5 or 2 for example the leading of the text.
Use the align functions to align to dartboard.
Use margins and column guides to position content.
Because adobe indesign layout pages can include column guides as well as margin guides you can establish the gutter dimensions for a variety of layout options within one set of guides.
Indesign uses the first definition in margins and columns so i m going to guess that is what your question is about.
Choose layout margins and columns.
Some people use gutter to describe the space between 2 columns other use it to describe the space between two pages.
Open the pages panel window pages and select the thumbnails for the pages you wish to change.
Gutters and full bleed.
Enter values for top bottom left and right margins as well as the number of columns and the gutter the space between columns.
Ungroup the object and select all the inner lines.
Gutter widths should relate to the body text leading value.