Why your browser canvas 'A4 export' may disappoint at the print shop

A developer building a browser-based collage tool discovered that labelling a canvas preset 'A4' only guarantees the correct aspect ratio, not a print-ready resolution. An HTML canvas works purely in pixels and has no built-in concept of physical size, so the actual print quality depends on how many pixels are exported relative to the paper dimensions. A 1414x2000px export yields just 171 DPI — acceptable for home printers but well below the 300 DPI expected by photo labs, which requires a 2480x3508px canvas carrying over 35 MB of raw bitmap data. High-resolution exports combined with multiple full-size source photos can silently crash browsers, particularly on lower-memory Android devices, making image downscaling on import a critical optimisation. The developer concluded that clearly communicating export resolution and its print suitability in the UI was more impactful than any code fix, since users accept known limitations but not surprises discovered after paying for prints.