Trim, bleed, safe inset, and raster dimensions
Bleed extends outside the trim on every side. The safe inset sits inside the trim. Raster dimensions round upward to whole pixels so the canvas meets at least the requested resolution.
To check the physical size supported by an existing raster image, use the Print Size Calculator before extending its artwork into the bleed.
The formula
Both the left and right edges add bleed to width, while top and bottom add bleed to height. The safe margin works in the opposite direction and is calculated from the finished trim rather than the larger artwork canvas.
Worked example
An A4 trim of 210 by 297 mm with 3 mm bleed needs artwork measuring 216 by 303 mm. A 5 mm safe inset leaves 200 by 287 mm for important content. At 300 PPI, the raster canvas is at least 2,552 by 3,579 pixels. US Letter is 215.9 × 279.4 mm. Adding 3.175 mm per edge gives artwork 222.25 × 285.75 mm, or 8.75 × 11.25 inches; at 300 PPI its canvas is 2,625 × 3,375 pixels.
How to use this calculator
- Choose a trim preset or enter custom width and height in millimetres.
- Choose custom, 3 mm or one-eighth-inch bleed; enter the safe inset in millimetres.
- Set PPI and read artwork, safe content, inch dimensions and the raster canvas.
Bleed is outside the finished page
Artwork intended to reach the paper edge must continue beyond the trim line. The extra material allows small cutting variations. Increasing canvas size without extending the background artwork does not create useful bleed; it can simply add an empty border that will appear at the cut.
Keep safe area separate from crop marks
A safe inset keeps important content away from the finished edge. It is a different measurement from bleed, and neither automatically supplies crop marks or a printer’s slug area. This tool assumes symmetric margins on all four sides. Facing-page booklets, inside-edge rules, binding allowances, and asymmetric specifications require a document setup suited to that job.
Presets without losing your custom dimensions
Trim presets supply A4, A5, US Letter or a 3.5 × 2 inch US business card, converted exactly to millimetres. Bleed presets use 3 mm or exactly 3.175 mm (one eighth inch) per edge. Those two bleed values are not identical and must follow the printer’s specification. Custom trim and bleed values remain saved when switching presets. Artwork and safe boundaries remain millimetres in the working table; added inch cards show the artwork dimensions. Raster pixels round upward.
Assumptions & limitations
What this calculation assumes
- Every edge uses equal bleed and equal safe inset.
What to keep in mind
- Excludes crop marks, slug, binding, imposition, and PDF box configuration.
Common questions
Can I use 3 mm for every printer?
Use the provider’s specification. The example is not a universal production requirement.
Why are the pixel dimensions rounded upward?
A raster cannot have fractional pixels. Rounding upward avoids creating a canvas slightly smaller than the requested physical size at the chosen PPI.
Sources & further reading
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