What font size should I use for a mini booklet

Hey Salma...

For product information use size 10pt or 11pt.

If the booklet is for children use 12pt to 14pt.

hope thats help!! 

~Alexandre 

Depends on the target audience: children's book, serious, funny, old age.

Depends on what font you are using, some look larger, some look smaller, some have bigger spacing, etc.

Depends on how many pages do you want to fill? 

Optimal line lengths would be approximately 50-60 characters including spaces. 

Arial font fits this at 8pt

Univers 39 Thin Condensed fits this at 18pt!

It's really open ended - but stick to optimal line lengths - tonnes of info online about it.

Plus 0.3cm for a margin is too tight for trimming if you are going to get this printed, consider a minimum of .5cm.

That depends on what typeface you are using, and how much information needs to go on each page. All I can say is that you should keep your type sizes for headlines, subheads and body text consistent throughout the booklet.