18 × 24 inch poster at 300 DPI is 5400 × 7200 pixels

The working

Pixels are inches multiplied by the resolution.

• Width: 18 in × 300 = 5,400, which rounds to 5400 pixels.
• Height: 24 in × 300 = 7,200, which rounds to 7200 pixels.

Bleed is extra image past the trim line, so that a cut that lands slightly off still leaves ink to the edge. Print shops usually ask for 0.125 in on every side of a US size, which makes the file 5475 × 7275 pixels.

Is your photo big enough?

To fill 18 × 24 inch poster at 300 DPI an image needs at least 5400 × 7200 pixels. Cropped to fill the sheet:

• A 12 megapixel phone photo (4000 × 3000) gives 167 DPI: short of 300, so it would be upscaled or printed softer.
• A 24 megapixel camera photo (6000 × 4000) gives 222 DPI: short of 300, so it would be upscaled or printed softer.
• A 48 megapixel photo (8000 × 6000) gives 333 DPI: enough.

At 300 DPI the pixels of a print blend together from about 11.5 inches (29 cm) away. 300 DPI is the standard for print that is held in the hand: books, magazines, photo prints, business cards and flyers. At reading distance the eye can no longer pick out the pixels.