Lastly set up the spine.
How to set createspace gutter.
Look at the back of paperback books for ideas and be careful to leave space for the barcode and trimming as per createspace instructions.
If you re using mirror pages the value for the inside margins will be set in the gutter field.
These both mean the same thing so you only need to set one.
If you go to the margins tab of the page setup dialog and select bookfold or mirror margins from the multiple pages drop down and then try increasing the gutter and then the inside margin you will see what affect each one has.
However traditionally gutter spines have also been the smallest of the margins since the recto and verso pages laid together each with a large gutter spine will create an unpleasingly blank look to the center of the book.
The gutter margins need to be sufficient so that the spine or the readers eyes are not strained while reading.
The spine of the book is calculated based on the number of pages and on the type of paper you plan to use.
So if you want the inside margin to be 0 5 for all pages add this value in the gutter margin box and leave the inside margin field blank.
The gutter is in addition to the inside margin.
Review your project setup.
Page extent minimum inside margin inches minimum inside margin mm 24pp 150pp.
For createspace you need to use the following measurements.
If you want a black white book published on white paper with up to 150 pages the spine will be the number of pages multiplied by 0 002252.