How to get an image to 300 dpi for printing

The arithmetic, once

Pixels needed equals print inches times dpi. A 4-inch chest logo at 300 dpi wants 1,200 pixels across. An 11-inch front print wants 3,300. A 12-inch square wants 3,600 each way, which is about 13 megapixels. Measure your file against that number and you have your answer — everything else is a distraction, including whatever dpi value the file claims.

Why the dpi field lies to you

Set a 900×900 JPG to 300 dpi and you have told the printer to lay it down three inches wide. Set the same file to 72 dpi and you have asked for twelve and a half inches of the same 900 pixels. Nothing about the image changed between those two; only the instruction did. This is the single most common reason a file that looked fine on screen prints soft.

When 300 is the wrong target anyway

It is a garment and signage rule of thumb, not a law. DTF and screen printing are comfortable at 300 at final size. A banner read from ten feet away is fine far below it, because the viewing distance does the work — large-format shops routinely output at 100 to 150. Chasing 300 on a six-foot banner produces an enormous file and no visible benefit.

What to do when you are short

Ask for the original first — a vector logo or the designer’s source file beats any reconstruction, every time, and costs nothing but an email. When that is not available, an upscale reconstructs detail rather than interpolating between pixels, which is what makes a photograph come back usable rather than merely larger. Type is the exception — letterforms can come back sharp but subtly misshapen, so set those from the font rather than upscaling them. Free here at up to 4 megapixels signed out and 8 with a free account, no watermark. Past 8 megapixels — a full 12-inch square at 300 — you are into credits.