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The Math of Folding Panels

I know what you’re thinking­–math, no, anything but math! But, don’t worry; it’s not that bad. Truth is, math is used in everyday situations more often than people realize. From figuring out your monthly budget to counting your cups of coffee, it’s everywhere, and it doesn’t compromise.

Today, we’re not doing anything too complicated. I’m going to discuss a few basic principles of folding panels for printed pieces. Why do we need math to figure folding panels? It’s a matter of physics. When folding a sheet of paper we must take into account the thickness of the paper itself, the air or gap between the folded sheets, the bunching up of the paper where it folds, and the folding mechanism. Some papers and folds may require different panel measurements than others, but for most products there is a single measurement we can apply to figure each panel, and that is 1/16 inch, or 0.0625”. This can be adjusted to 0.06”, 0.065”, or 0.07” if desired, but for purposes of using an American standard ruler we will use 0.0625”.

When a sheet of paper is folded into a basic trifold format there are two different panel measurements. The two outside panels (the front panel and back panel when folded) are the same width. The inside panel (the one that folds in first) must be slightly shorter so that it does not bunch up against the opposite fold.

In this example of a 9” x 12” trifold brochure (Figure 1), the outside panels are exactly 4” with inside panel being 0.0625” shorter, allowing the piece to fold to 4” and making the actual flat trim size 9” x 11.9375”.

Another way to fold this piece is to fold it to something slightly larger than 4” so that we retain the flat trim size of 9” x 12” (Figure 2). In this example the outside panels fold to 4.023” with the inside panel being 3.954”. This may seem like a simpler solution, however, it can be problematic if the artwork does not take into account the folding aspects and is designed with even panels. It is often simpler for production to trim the inside panel short rather than adjust or stretch the outside panel graphics in prepress to accommodate the fold.

There are times when one or the other of these solutions is preferred. Typically, for a standard 8.5” x 11” trifold we will keep the flat trim size at 8.5” x 11” making the finished folded size 3.6875” and adjust the artwork accordingly. For an 8.5” x 25.5” trifold we will usually trim the inside panel short so the piece folds down to 8.5” x 11”. For brochures with more panels that fold in formats like roll fold, double-parallel, gate-fold, or even iron cross, the general rule is that each panel be consecutively 0.0625” shorter than the next. A double-parallel fold would have the two outside panels the same width and the two inside panels the same shorter width. A gate-fold piece would have the two center panels the same width and the two outer panels the same shorter width.

In all cases the finished size will be determined by the artwork and the ability to adjust, if needed, in prepress. Adequate bleed and proper panel sizes allow the bindery to obtain proper folds and produce a quality finished product. Contact Phillips prepress if you have any questions regarding designing for print. We’re here to help.