To find the correct size, a rule of thumb is "10 sheets of 20 lb stock for each millimeter of spine width" . This is only a guideline because sheet thickness can vary from manufacturer to manufacturer. It is always best to first measure the thickness of the actual contents. Measure with the sheets loosley stacked rather than pinched tight. A slightly larger cover will always work, but you can't get a smaller cover to hold more pages than the width of its' glue strip. For instance, if you have 32 pages you will need to go up to 4mm.

If you are caught in between sizes, you can try fanning the pages at the spine side before placing them into the covers so there is not a big gap in the front or back. This also allows the glue to wick up into the page so it's not just holding on the very edge. If you have to use a cover that you know is just a bit too big, you can still get a nice crisp appearance by laying it down on a flat surface after it has been removed from the binding machine, and running a smooth block, or ruler over the spine to cause it to have an even crease. This just takes a few seconds.

One more thing: Some binding machines come with a built in cover gauge.
These aren't always accurate. It's always best to measure the actual stack of contents.

If you ever have "quality control" problems call 1-508-992-4144 or email us anytime and we'll be glad to advise you.

Spine Type Determine By Number Of Sheets