{
  "id": 2028289,
  "title": "Your canvas \"A4 export\" is not A4: DPI, print size, and the number nobody checks",
  "url": "https://urgent.news/2026/08/19/your-canvas-a4-export-is-not-a4-dpi-print-size-and-the-number-nobody",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-08-19T22:12:08.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/bellsal_b44bf6d/your-canvas-a4-export-is-not-a4-dpi-print-size-and-the-number-nobody-checks-5akh"
  },
  "original_language": "en",
  "account": "When adding an A4 preset to a browser-based collage tool, it wasn't the initial layout calculations that proved challenging. The real hurdle was understanding that A4, in the context of a canvas, is a shape rather than a fixed size. This misconception often catches users when they attempt to print their creations. The focus should be on the numbers that matter. A canvas is merely a grid of pixels, with no inherent physical dimensions. The connection between the canvas and physical paper is established through DPI (dots per inch). However, the canvas itself has no inherent understanding of this relationship. Thus, when a preset suggests A4, it can only honestly guarantee the aspect ratio, which is 1:1.414 for all ISO 216 paper sizes. The actual pixel dimensions of the exported image depend entirely on the number of chosen pixels. For instance, if the preset exports 1414 x 2000 pixels, this provides the correct A4 aspect ratio. To translate this to inches, you would divide the pixel dimensions by 300 DPI, resulting in a print size of 4.72 x 6.69 inches, which is slightly under the standard A4 size. For optimal results with home or office printers, aiming for 300 DPI is generally acceptable. To achieve this, you would need approximately 2480 x 3508 pixels, which is significantly more than the initial 1414 x 2000 pixels. This trade-off is crucial because it directly impacts the print quality and the amount of memory required. One could argue that exporting at 300 DPI would eliminate this issue, but doing so would require more memory and might not be feasible due to other constraints, such as the limitations of phones where the tool is often used. The solution came in the form of downscaling source images on import. By setting a maximum source edge length of 2400 pixels, the tool ensures that the memory pressure is reduced without noticeable visual degradation. This approach also helps prevent memory crashes that are commonly experienced on Android devices. It's important to note that the issue extends beyond just technicalities. Users are typically frustrated because they expect 'A4' to mean a paper size that will print correctly, but they are often left in the dark about the actual print size and DPI. A clear communication in the user interface, stating the export size in pixels, the approximate DPI at A4, and explicitly indicating that this is suitable for home printing rather than professional photo labs, can mitigate user frustration. Additionally, it's worth informing users about printer margins and the orientation of their images. Most home printers cannot print to the edge of the paper, and users may find that their compositions are centred differently when printed. Furthermore, since the canvas used for designing is in portrait orientation, users seeking landscape A4 layouts need to adjust their dimensions accordingly. The key takeaway is simple: if you export any content intended for paper from a canvas, perform this arithmetic once and include the result in your interface. Calculate the DPI by dividing the pixel width by the physical width in inches. This straightforward step can make the difference between a tool that users trust and one that they abandon after a disappointing print.",
  "summary": "When I added an \"A4\" preset to a browser-based collage tool, I thought the hard part was the layout maths. It wasn't. The hard part was that \"A4\" on a canvas is a shape, not a size — and if you don't say that out loud, your users find out at the print shop. Here is what I got wrong, and the numbers that matter. A canvas has no physical size An HTML canvas is a pixel grid. It has width and height…",
  "key_points": [
    "A4 in canvas tools represents a shape, not fixed size",
    "DPI determines physical print size, not canvas",
    "Exporting 1414x2000 pixels yields ~4.72x6.69 inch A4"
  ],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}