Use the transform panel to determine the exact with and height of your outer margins.
Indesign margin and gutter.
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.
Assuming i guessed correctly are you trying to define the gutter width or gutter position.
Gutter widths should relate to the body text leading value.
Indesign uses the first definition in margins and columns so i m going to guess that is what your question is about.
To adjust column guides manually drag them horizontally to new positions producing unequal widths.
Open the pages panel window pages and select the thumbnails for the pages you wish to change.
0 5 inch margins become 0 625 inch from there drop your content and get to formatting.
Choose layout margins and columns.
Ungroup the object and select all the inner lines.
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.
Use the align functions to align to dartboard.
Enter values for top bottom left and right margins as well as the number of columns and the gutter the space between columns.
210x297 less 10mm each side would be 190x277.
When you re done and you export your pdf you ll have it sized and ready for full bleed printing.
Gutters and full bleed.
Planning your indesign pages using margins and columns bookmachine this is an excerpt from nigel french s book indesign type.