The trouble you have with this is mainly connected with the depth of the book block which will vary considerably with the thickness of each page. I can help you with this but you need to find out what the GSM of the pages you are using. I use 90 GSM (grams per square metre) for most of my books, for poetry books which tend to have far fewer pages,I tend to use 120 GSM.
Most ordinary office duplication papers are only 80 GSM.
To give you an example, I have a book which has 168 pages of 90 GSM offset paper. With endpapers it is 172 pages thick. I needs a spine thickness of 1.331 cm. If it had 270 pages at 90 GSM it would need:
1.331 over 172 times 270 to give the thickness of the spine, that will be 2.01cm, And that's the thickness of the pages in the book.
For an A5 format book you will need to use a measurement than can fit twice the A5 width (148.5cm) plus the thickness of the pages (the spine) into the length by the height (210 cm) for the width. It will also help if you can let me know how you intend binding the book, hard cover or paperback.
If you let me know at millrind (at) btinternet.com , sorry these measurememnts are in metric, that's the way the UK goes at the moment.
John

 

To respond your questions first the paper will probably be #60 and it’s gonna be a hard cover book. I plan the design of my spline so I can further adjust it if I have more pages or change the grade of the pages. To explain its because I want a cover with a quite complex design and I want to start to work on the layout of the different elements. So if I can get the spine right it would be cool but for now it’s not my main concern. Thanks for your answers

 

What I didn't say is what I should have said is that your biggest problem in printing your book is that you want to print to an A5 on copy paper. Your greatest problem is going to be that folded copy paper will not give you the proper grain direction for an A5 book. This means that however many sheets you print, they will never lie properly flat. All paper you can buy, whether letter size of A4 size will be long grain. What you need for an A5 book is make sure that the sheets that you start with short grain so that when they are folded in half the A5 finished printed sheet will have the grain running top to bottom. The only way you are likely to get this sort of paper is if you tryto buy it buy it from a printer.
I get these sheets directly from a paper dealer in Scotland but I have to buy them as 4 reams at a time which are A4 cut from A2 sheets of paper.
You are never going to be happy with your result if you don't make sure of this, however much work you put into it
I should add that I can only supply you with a template if I know the answers to these questions.
Are you using an apple or a windows OS?
What software will you be using to print the book, are you using a DeskTopAuthoring Program?
What sort of printer do you have? and
Are you intending to traditionally bind your book or try to perfect bind it?
Sorry for this but I have found that few videos or websites tell you these important facts, they only want to sell what they have got.
If you are interested I have put a couple of free books on line you might find interesting.
John Kay

 

What I didn't say is what I should have said is that your biggest problem in printing your book is that you want to print to an A5 on copy paper. Your greatest problem is going to be that folded copy paper will not give you the proper grain direction for an A5 book. This means that however many sheets you print, they will never lie properly flat. All paper you can buy, whether letter size of A4 size will be long grain. What you need for an A5 book is make sure that the sheets that you start with short grain so that when they are folded in half the A5 finished printed sheet will have the grain running top to bottom. The only way you are likely to get this sort of paper is if you tryto buy it buy it from a printer.
I get these sheets directly from a paper dealer in Scotland but I have to buy them as 4 reams at a time which are A4 cut from A2 sheets of paper.
You are never going to be happy with your result if you don't make sure of this, however much work you put into it
I should add that I can only supply you with a template if I know the answers to these questions.
Are you using an apple or a windows OS?
What software will you be using to print the book, are you using a DeskTopAuthoring Program?
What sort of printer do you have? and
Are you intending to traditionally bind your book or try to perfect bind it?
Sorry for this but I have found that few videos or websites tell you these important facts, they only want to sell what they have got.
If you are interested I have put a couple of free books on line you might find interesting.
John Kay

ok thanks for the efforts you're putting in but i will find elsewere or do it myself in the worst case because it seem that im not understood. i just want to do a daft of the element on the cover of the book and not have it in 3 separate document. in fact the template in question could even be for a letter size book i can deal with it later for now i only want a visual representation of the work and word thats gonna be on the cover. again thank you to have try
wishing you the best
Régis

 

I just want to know what progam you are going to use to print out the book cover. I can supply the template in Affinity Publisher or MS Publisher or MSWord or LibreOffice format. I do need to know which.
I may have a problem if you are using an Apple computer however.
John

 

I posted and being helped somewhere else meanwhile and I been supply the template I need , again thanks

 

Sorry I wasn't more help to you, I am curious to know however what the type of file you were supplied with.
John

 

PNG and other . I mostly plan on using png taught