Choosing Resolution and Scale for PDF Exports
The scale slider is the single most consequential setting in the converter, and it is the one most often left at its default. This guide explains what the numbers mean, what they cost, and how to pick one deliberately.
What scale actually means
PDF pages are measured in points. One point is defined as 1/72 of an inch, so an A4 page is about 595 by 842 points and US Letter is 612 by 792. When the converter renders at scale 1x, it produces one pixel per point, which works out to exactly 72 pixels per inch.
Every step up multiplies that. Scale 2x gives 144 DPI, 3x gives 216 DPI, 4x gives 288 DPI, and scale 10x reaches 720 DPI. So although the slider is labelled as a multiplier, you can read it as a DPI setting by multiplying by 72.
What it costs
Scale applies to both dimensions, so the number of pixels grows with its square. An A4 page is roughly half a megapixel at 1x, two megapixels at 2x, eight megapixels at 4x, and around fifty megapixels at 10x. File size and rendering time follow that curve fairly closely.
This is why reaching straight for the maximum is a poor default. Scale 10x on a hundred-page document asks your browser to render fifty-megapixel bitmaps a hundred times over, and the resulting archive can be enormous, all for detail that will never be visible in the intended use.
Picking a value by purpose
For thumbnails and small previews, 1x is genuinely adequate. For viewing on a normal screen, or for embedding a page into a slide or a document, 2x is the sensible baseline; it is sharp at typical viewing sizes and the files stay manageable.
For a high-resolution display, or when someone might zoom in, 3x to 4x gives you room to spare. For printing, aim for 4x or higher: around 288 DPI is acceptable for body text, and pushing to 5x gets you to 360 DPI, which is comfortable for most office printing.
The upper end of the slider is for archival work, for pages with very fine engraving or small print that must stay legible under magnification, and for cases where the output will be downsampled later. Outside of those, it mostly produces large files.
Resolution and format together
Resolution and format are not independent decisions. If you need a high scale but the archive is getting unwieldy, switching from PNG to WEBP or to a high-quality JPG will usually save more space than dropping a scale step, and it costs less visible detail.
Conversely, if a page still looks soft after you raise the quality setting, quality is not the problem. Encoder quality cannot recover detail that was never rendered in the first place. Raise the scale instead.
A practical approach
Work out the physical size the image will be displayed or printed at, multiply by the DPI that context needs, and pick the smallest scale that reaches it. In practice this means 2x for most screen use and 4x for most print use, with the extremes reserved for the cases that genuinely call for them. Converting a single page as a test before running the whole document takes a few seconds and saves a lot of guessing.
How to convert a PDF to an image