The Poster 18x24 size (5400×7200px)
An 18 by 24 inch poster is one of the most popular large-format sizes, and at a full 300 DPI it works out to 5400 by 7200 pixels. This is the size used for event posters, gig flyers, movie-style prints, gallery pieces, and retail signage, big enough to command a wall while still fitting standard 18x24 frames. Its 3:4 aspect ratio is a classic portrait poster shape that suits stacked layouts of image, title, and details.
At poster scale, resolution and viewing distance interact. A 300 DPI file at 5400x7200 looks flawless up close, which is ideal for gallery and retail prints people inspect nearby; for posters mainly viewed from across a room, some printers accept 150 to 200 DPI, but starting at the full 300 gives you the most flexibility and the sharpest result. The trap to avoid is upscaling a small image to these dimensions, which prints as visible softening no matter how good it looked on screen.
Plan bleed and safe margins carefully because errors are magnified at this size. Extend background artwork a few millimeters past the 18x24 trim so no white edge shows after cutting, keep titles and logos well inside a safe margin, and consider how a frame's lip will overlap the outer edge. Large files also get heavy, so a correctly sized 5400x7200 export avoids sending an unnecessarily massive image. Everything here resizes 100% in your browser with no upload and for free, so your artwork stays private. Print shops differ on DPI, bleed, and color, so confirm before ordering.