What is DPI? Dots per inch, PPI and the numbers that matter
DPI explained in plain terms: what the number means, how it differs from PPI, why 300 dpi is the print standard, why 72 dpi is a myth for screens — and how to work out the pixels you need.
DPI stands for dots per inch. It describes how many individual dots a printer lays down along one inch of paper — the higher the number, the finer the print. In everyday use the term is also applied to digital images, where it strictly should be PPI, pixels per inch: how many of an image’s pixels are packed into one inch when it is displayed or printed. Both numbers answer the same question — how big does each pixel end up in the real world?
The key thing to understand is that DPI is not a property of the pixels themselves. A 3000 × 2000 photo contains exactly the same information whether its file says 72 or 300 dpi; the number only changes how large a printer will make it: 41.7 × 27.8 inches at 72 dpi, 10 × 6.7 inches at 300 dpi.
Common DPI values and what they are for
| Value | Typical use | What it means for a 10 × 15 cm print |
|---|---|---|
| 72 dpi | legacy screen value, “web” exports | only 283 × 425 px — visibly blurry in print |
| 96 dpi | Windows / CSS reference resolution | 378 × 567 px — still too soft for print |
| 150 dpi | posters, banners, large prints | 591 × 886 px — fine from a distance |
| 300 dpi | photo prints, brochures, magazines | 1181 × 1772 px — the standard |
| 600 dpi | fine line art, small text, stamps | 2362 × 3543 px — rarely needed for photos |
Pixel counts are width × height for a 10 × 15 cm (4 × 6 in) print at each resolution: 4 in × dpi by 6 in × dpi.
DPI vs PPI: the difference
PPI describes an image or a screen: a 27-inch 4K monitor packs 3840 pixels into about 23.5 inches of width, so it has roughly 163 ppi. DPI describes the printer: an inkjet might place 1440 dots per inch, using several dots of different colours to reproduce one image pixel. When a print shop asks for “300 dpi”, they mean 300 image pixels per printed inch — technically PPI. Because the two are used interchangeably almost everywhere, imagenimble’s converter treats them as the same number.
Why 300 dpi is the print standard
At normal reading distance the human eye stops distinguishing individual dots at roughly 300 per inch, so 300 dpi prints look continuous. Below about 200 dpi pixels start to show as softness; below 150 they become visible blocks on anything held in the hand. Large prints are the exception: a poster seen from two metres can be printed at 150 dpi, a billboard at 20 dpi, because distance does the smoothing.
To check whether an image is print-ready, divide its pixel width by the intended print width in inches. 2400 pixels for an 8-inch print gives 300 dpi — ideal. 1200 pixels for the same print gives 150 dpi — acceptable for a poster, not for a photo book.
Why 72 dpi for the web is a myth
The idea that “web images are 72 dpi” dates from the original Macintosh, whose 72-ppi screen matched 72-point type at actual size. Modern screens range from about 96 ppi on a desktop monitor to over 450 ppi on a phone, and no browser reads the DPI value in a file — it displays the image pixel for pixel (or scaled to fit the layout). Saving a web image at 72 dpi does nothing for file size; what matters is the pixel dimensions and the compression. Use the compressor for that, not the DPI field.
Changing DPI without changing pixels
Image editors offer to change resolution with or without resampling. Without resampling, only the label changes: a 3000 × 2000 file becomes a smaller print, nothing is lost. With resampling, the editor invents or discards pixels to hit a target size — enlarging this way adds no real detail and makes the image softer. The safe route for print is always to start from the largest original you have and let the converter tell you the achievable print size at 300 dpi.
Frequently asked questions
Dots per inch — the number of printer dots placed along one inch of paper. For digital images the equivalent is PPI, pixels per inch; in practice both terms are used for the same value.
Yes — 300 dpi is the standard for photo prints and professional printing. Anything held in the hand should be 300 dpi; large posters can go down to 150 dpi.
Not on its own. DPI only sets how large the pixels print. Real quality comes from the number of pixels; changing DPI without resampling does not add detail.
It does not matter — browsers ignore the DPI value. Choose the pixel dimensions the layout needs and compress the file well.
Multiply the print size in inches by the DPI: 8 in × 300 dpi = 2400 px. For centimetres, divide by 2.54 first. The pixels-to-inches converter does this for any size.