What size bleed does an A3 poster need?
A standard A3 poster is printed portrait with a 297 × 420 mm trim size and needs a 3 mm bleed on every edge, which makes the artwork board 303 × 426 mm and keeps important text and logos inside a 291 × 414 mm safe area.
The numbers
- Trim
- 297 × 420 mm
- Bleed box
- 303 × 426 mm
- Safe area
- 291 × 414 mm
- Page
- 309 × 432 mm
- The bleed box adds the 3 mm bleed to every edge of the trim, so 297 + 3 + 3 = 303 mm wide and 420 + 3 + 3 = 426 mm tall, giving a 303 × 426 mm bleed box.
- The safe area pulls the same 3 mm in from every edge of the trim, so 297 − 3 − 3 = 291 mm wide and 420 − 3 − 3 = 414 mm tall, giving a 291 × 414 mm safe area.
- The page adds room for crop marks on top of the bleed, so 297 + 6 + 6 = 309 mm wide and 420 + 6 + 6 = 432 mm tall, giving a 309 × 432 mm page.
- Bleed is only added once per edge, so the 3 mm bleed setting adds 6 mm to the total width and 6 mm to the total height, not 3 mm.
The most common mistake is building the artwork at exactly 297 × 420 mm with no bleed at all, so any background colour or image stops right at the trim line and a sliver of white paper shows up along one or two edges after the poster is cut.
Crop marks sit outside the bleed box, which is why the full page ends up at 309 × 432 mm even though the finished poster is only 297 × 420 mm.
Keep the safe area margin in mind for anything you do not want trimmed off, since cutting during production can shift by a fraction of a millimetre in either direction.
Guides are placed in a PDF optional-content layer flagged not to print, so they stay visible on screen but are omitted when the file is printed.
- Bleed303 × 426 mm
- Trim297 × 420 mm
- Safe area291 × 414 mm
| Box | mm | pt |
|---|---|---|
| Bleed box (make artwork this big) | 303 × 426 mm | 858.9 × 1207.56 pt |
| Trim (final cut size) | 297 × 420 mm | 841.89 × 1190.55 pt |
| Safe area (keep text inside) | 291 × 414 mm | 824.88 × 1173.54 pt |
| PDF page (MediaBox) | 309 × 432 mm | 875.91 × 1224.57 pt |
- Trim
297 × 420 mm- Bleed box
297 + 2 × 3 = 303 mm wide, 420 + 2 × 3 = 426 mm tallBleed is added here, and only here. Setting your document page size to the bleed box (303 × 426 mm) and then adding bleed again in your design software double-counts it, leaving a white gap at the crop marks.
- Safe area
297 - 2 × 3 = 291 mm wide, 420 - 2 × 3 = 414 mm tall- Marks
3 mm long, offset 3 mm from the trim edge- Page
297 + 2 × 6 = 309 mm wide, 420 + 2 × 6 = 432 mm tallThe page (309 × 432 mm) is larger than the bleed box (303 × 426 mm) so it has room for the crop and registration marks; the artwork itself does not need to fill the page.
The generated PDF is a correctly sized blank canvas: a page with MediaBox, TrimBox, and BleedBox set to the dimensions you specify, plus crop marks showing where to cut. It does not contain any artwork.
Colour in the PDF is plain RGB or grayscale and is not colour-managed.
Confirm the bleed value with your printer before sending final artwork.