A7 at 72 DPI is 210 × 298 pixels

The working

Pixels are inches multiplied by the resolution, and an inch is 25.4 mm.

• Width: 74 mm ÷ 25.4 = 2.913 in; 2.913 in × 72 = 209.8, which rounds to 210 pixels.
• Height: 105 mm ÷ 25.4 = 4.134 in; 4.134 in × 72 = 297.6, which rounds to 298 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 3 mm on every side of an A-series page, which makes the file 227 × 315 pixels.

Is your photo big enough?

To fill A7 at 72 DPI an image needs at least 210 × 298 pixels. Cropped to fill the sheet:

• A 12 megapixel phone photo (4000 × 3000) gives 968 DPI: enough.
• A 24 megapixel camera photo (6000 × 4000) gives 1,373 DPI: enough.
• A 48 megapixel photo (8000 × 6000) gives 1,935 DPI: enough.

At 72 DPI the pixels of a print blend together from about 47.7 inches (121 cm) away. 72 DPI is the old screen convention: early Macintosh displays showed 72 pixels to the inch, matching the 72 points in an inch of type. Many image files still carry a 72 DPI tag for that reason.