Trim size & bleed

The trim size is the size of your finished product (Letter, A4, a 3.5 × 2 in business card …). The document size is slightly larger, because bleed is added all around. In short: document size = trim size + bleed on every side. Common bleed values are 1/8 inch (0.125 in) in the US and 3 mm in Europe.

Why bleed? Printers cut a stack of sheets at once, and the cut can shift by a fraction of a millimeter. If your background stops exactly at the edge, a thin white line can appear. Extend backgrounds and edge-to-edge images into the bleed, and that can't happen. PreflightPilot checks whether your PDF has bleed and whether the trim size is marked (TrimBox).