What Pixel Size Should an Image Be? Web, Email, Print and DPI Explained

For print, multiply the size in inches by the resolution you want: 300 pixels per inch for photos viewed up close, 150 for posters and anything seen from a metre or more away. A 4 × 6 inch print therefore wants 1,200 × 1,800 pixels. For screens, the answer is about twice the size the image is displayed at, because most phones and many laptops pack two or three device pixels into each point of layout. A picture shown 700 pixels wide in an article should be around 1,400 pixels wide.

The tables below give the numbers for common paper sizes and on-screen spots, and the sections after them explain where the rules come from so you can work out any size that is not listed.

Pixels needed for common print sizes

Each figure is the size in inches multiplied by the dots per inch (DPI, or more precisely pixels per inch, PPI), rounded to the nearest pixel. Paper sizes defined in millimetres were converted at 25.4 mm to the inch.

Run it in reverse to see how big an image you already have can print. A 12-megapixel photo of 4,032 × 3,024 pixels gives 13.4 × 10.1 inches at 300 DPI, or twice that in each direction at 150 DPI. So almost any modern phone photo is enough for an A4 print; the thing that limits quality is usually focus and light, not pixel count.

What DPI actually means

A digital image has only one real size: its width and height in pixels. The "DPI" number stored inside a JPEG or PNG is a note that says how many of those pixels should go into each printed inch. Changing it from 72 to 300 in an editor, without resampling, does not add a single pixel or change the file's sharpness. It only changes the default print size, from very large to smaller.

That is why a request for "a 300 DPI image" is incomplete on its own. What the print shop really needs is enough pixels for the size it will print. A 600 × 400 pixel image labelled 300 DPI is still a 2 × 1.3 inch print at that quality. When someone asks for 300 DPI, ask for the print size too, then use the table above.

Why 300 and why 150?

At a normal reading distance of around 30 cm, people with good eyesight stop being able to see individual dots somewhere around 300 per inch, which is why it became the standard for photo prints and magazines. The further away the viewer, the lower the density that still looks sharp: a poster read from two metres away at 150 DPI looks as crisp as a handheld print at 300.

Screens: CSS pixels and device pixels

Web pages are laid out in CSS pixels, a unit that stays roughly the same physical size on every screen. A high-density display fits two or three device pixels into each CSS pixel in both directions; browsers report this ratio as window.devicePixelRatio. An image 700 pixels wide shown in a 700-CSS-pixel column on a density-2 phone is stretched across 1,400 real pixels and looks soft. Supplying a 1,400-pixel image fixes that.

Going to 3x rarely pays off for photographs. The file roughly doubles again compared with 2x, and at arm's length few people can see the difference. For photos, 2x is the practical ceiling; for logos and icons, use SVG so the question never comes up. Pages can also list several widths with the srcset attribute and let each device download the one it needs.

Recommended widths for common places

These are working defaults, not rules. The 600-pixel email column is a long-standing convention because many mail programs render messages in a narrow pane, and 2,048 pixels for attachments is large enough to fill a laptop screen while staying at a few hundred kilobytes as a JPEG.

Aspect ratio: the other half of "size"

Pixel count is only part of the job; the shape matters too. Phone cameras usually shoot 4:3, many digital cameras 3:2, and screens and video are 16:9. A 4 × 6 inch print is 3:2, so a 4:3 phone photo will be cropped or bordered to fit it. An 8 × 10 print is 5:4 and loses even more from the long side. Crop deliberately before you export, choosing what to cut, rather than letting a print service or a web layout crop the middle for you.

• 1:1 square: profile pictures and product grids.
• 4:3: most phone photos and older presentation slides.
• 3:2: 4 × 6 prints and many dedicated cameras.
• 16:9: widescreen displays, video frames and modern slides.
• 1.91:1 (1,200 × 630): the usual shape for link previews.

Upscaling will not rescue a small image

Making an image bigger in pixels only interpolates between the pixels you already have; it cannot invent detail. A 640-pixel image enlarged to 1,920 pixels is larger on disk and still looks soft, just smoothly so. Newer machine-learning upscalers can produce convincing texture, but that detail is guessed rather than recorded, which matters for documents, evidence and product photos. When the source is too small for the print size you want, choose a smaller print or accept a lower DPI.

A quick way to decide

1. Find out the largest size the image will be shown or printed at.
2. For print: inches × 300 (close viewing) or × 150 (distant viewing).
3. For screens: displayed CSS width × 2.
4. Crop to the right aspect ratio, then resize to that width.
5. Compress for file size last; our guide to choosing between JPEG, PNG and WebP explains which format keeps the most quality for the bytes.