18 × 24 inch poster at 600 DPI is 10800 × 14400 pixels

The working

Pixels are inches multiplied by the resolution.

• Width: 18 in × 600 = 10,800, which rounds to 10800 pixels.
• Height: 24 in × 600 = 14,400, which rounds to 14400 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 10950 × 14550 pixels.

Is your photo big enough?

To fill 18 × 24 inch poster at 600 DPI an image needs at least 10800 × 14400 pixels. Cropped to fill the sheet:

• A 12 megapixel phone photo (4000 × 3000) gives 167 DPI: short of 600, so it would be upscaled or printed softer.
• A 24 megapixel camera photo (6000 × 4000) gives 222 DPI: short of 600, so it would be upscaled or printed softer.
• A 48 megapixel photo (8000 × 6000) gives 333 DPI: short of 600, so it would be upscaled or printed softer.

At 600 DPI the pixels of a print blend together from about 5.7 inches (15 cm) away. 600 DPI is used for line art, small text and scans that will be enlarged. It is also the native resolution of many office laser printers.