How can I make a file 300 dpi?

You can change an image's DPI in most graphics packages, and you can even do it in Preview on a Mac. Below are three basic approaches that cover the common tools, but remember that raising dpi works best when the image already has enough pixels to support the size you want to print.

• Photoshop: open Image and Image Size, uncheck Resample, and set the resolution to 300 dpi to see the true print size.
• Preview on Mac: open Tools and Adjust Size, uncheck Resample, and enter 300 in the resolution field.
• Export from a design app: when saving your PDF, set the export resolution to 300 dpi at final size.

Two related tips: images that print to the very edge should hit 300 dpi at bleed size, not just trim size, so they stay sharp after trimming, and logos or shapes built as vector art scale to any size without losing quality.

If lowering the dimensions is what brings the file to 300 dpi, the image is simply too small to print larger at full quality. Enlarging it adds pixels but not real detail, so you will need a higher-resolution original.

To see how large a file can print sharp, divide its pixel width by 300: a 1,000 px wide image prints cleanly at about 3.3 inches wide, 1,800 px at about 6 inches, and 3,600 px at about 12 inches. AI upscaling tools can help in a pinch, but they invent fine detail rather than recover it.