#### ReflexBlueHorror

##### Active member

I'm coming at this as a graphic designer --- someone without imposition software for offset printing, or enough knowledge (yet!) on sheet imposition.

I'm looking at formulas for determining the possible Section Folds+Trim Sizes for different sheet sizes from different mills (eg 530x760mm GS; 660x1016 GL; 720x1020 GL etc)

The formula I've been given from a book production manual is to:

1. Divide the sheet according to the section folds (eg 1020mm x 720mm GL folded to make a 32pp section = 180mm x 255mm Portrait)

2. Subtract trimming: 6mm height (-3mm top and -3mm bottom) and -3mm edge. Subtract a further -3mm from the width if the book is to be perfect bound.

The result is the maximum Trim Size for that imposition: a 1020 x 720 sheet can make 32pp section 177mm x 249 Portrait (Case sewn)

I can't see how this is right. At the very least it doesn't account for Gripper Margins. It doesn't mention bleeds either. Surely there must be a 'safe' standard allowance for the Gripper Margin too.

I'm posting here hoping that someone might know a better formula!

Thanks