The Math of Folding Panels

A Simple Guide for Print Design

I know what you’re thinking—math! But don’t worry; it’s not as bad as it seems. In reality, math shows up in everyday situations more often than you might realize. From managing your budget to counting your cups of coffee to improving print design, math is all around us, and it doesn’t have to be intimidating.

In today’s post, we’ll explore some basic math principles used when folding panels for printed pieces. Understanding how to fold panels requires math because of the physical properties of paper. There are several factors to consider, including the thickness of the paper, the gap between folds, the paper bunching at the crease, and the folding mechanism. While some papers and folds may need unique measurements, a general rule we can apply is 1/16 inch (or 0.0625”). This measurement can be adjusted slightly to 0.06”, 0.065”, or 0.07” if necessary, but we’ll use 0.0625” for consistency with American standard rulers.

Basic Principles of Folding Panels

When folding a sheet of paper into a basic trifold format, there are two types of panels: the outside panels and the inside panel. The outside panels—usually the front and back panels when folded—are the same width. The inside panel, which folds in first, must be slightly shorter to avoid bunching against the opposite fold.

Example: A 9” x 12” Trifold Brochure

Let’s look at a 9” x 12” trifold brochure (see Figure 1). In this case, the outside panels each measure 4”, while the inside panel is 0.0625” shorter to allow the piece to fold neatly. This results in a final flat trim size of 9” x 11.9375”.

Another option is to fold the outside panels to slightly more than 4” to retain the original 9” x 12” trim size (see Figure 2). For instance, the outside panels may fold to 4.023”, and the inside panel to 3.954”. While this solution may seem simpler, it can create issues if the artwork doesn’t consider the fold. In such cases, it’s usually easier to trim the inside panel shorter rather than stretch or adjust the graphics of the outside panel during prepress.

When to Choose Each Folding Solution

Which method you choose depends on the specific needs of your project. For a standard 8.5” x 11” trifold, we typically keep the flat trim size at 8.5” x 11”, resulting in a finished folded size of 3.6875”. We then adjust the artwork to fit the fold. On the other hand, for an 8.5” x 25.5” trifold, we would usually trim the inside panel shorter, allowing the piece to fold down to 8.5” x 11”.

Multi-Panel Folds: Guidelines and Best Practices

For more complex brochures with multiple panels, such as roll folds, double-parallel folds, gate folds, or iron cross folds, the general rule is to make each panel 0.0625” shorter than the next.

• A double-parallel fold has two outside panels the same width and two inside panels that are slightly shorter.
• A gate fold features two center panels of equal width, with the two outer panels being the same shorter width.

The Importance of Artwork and Prepress Adjustments

Ultimately, the finished size of any folded piece is determined by the artwork and any necessary prepress adjustments. Having adequate bleed and proper panel sizes is crucial for the bindery to make precise folds and produce a high-quality final product.

If you have any questions about designing for print or need help with your folding panel projects, don’t hesitate to reach out to Phillips Prepress. We’re here to assist with any print design needs!