Pixels per inch, viewing distance and print size
A digital photo is a grid of pixels and a print is a sheet of paper, so the link between them is pixels per inch, written ppi: pixels = inches × ppi. Printer makers talk about dots per inch, dpi, which describes the printer's own dots; ppi describes the image you give it. In everyday use the two are mixed up, and print labs mostly ask for the ppi of the file.
How many ppi are enough depends on how close the viewer stands. A common guide gives three hundred for a print held in the hand, two hundred to two hundred and fifty for one seen from one to two feet, one hundred and fifty from two to four feet, and one hundred from four feet or more. These are conventions, not limits of any printer.
The distance rule has a physical reason. Normal vision resolves two points about one minute of arc apart, roughly one point seven five millimeters at six meters. A pixel stops being visible when it spans less than that, so the ppi that matter are one divided by the distance times the tangent of one minute of arc: about three thousand four hundred divided by the distance in inches. At twelve inches that is about two hundred and eighty-six ppi, at six feet about forty-eight.
Two cautions. The tool takes the pixels of the file you will print: a photo cannot gain detail that the camera did not record, so upscaling does not help. And the viewing distance is where the pixels stop being resolved, not where the picture stops looking good; a print can be pleasant from closer.
Chart: pixel width needed by print width and resolution
Each cell is the width in pixels the photo needs for the print width in its row at the pixels per inch in its column. The height follows from the shape of the print.
| Pixels per inch | ||||
|---|---|---|---|---|
| Print width | 100 ppi | 150 ppi | 200 ppi | 300 ppi |
| 6 in | 600 px | 900 px | 1,200 px | 1,800 px |
| 8 in | 800 px | 1,200 px | 1,600 px | 2,400 px |
| 10 in | 1,000 px | 1,500 px | 2,000 px | 3,000 px |
| 12 in | 1,200 px | 1,800 px | 2,400 px | 3,600 px |
| 16 in | 1,600 px | 2,400 px | 3,200 px | 4,800 px |
| 20 in | 2,000 px | 3,000 px | 4,000 px | 6,000 px |
| 24 in | 2,400 px | 3,600 px | 4,800 px | 7,200 px |
| 36 in | 3,600 px | 5,400 px | 7,200 px | 10,800 px |
Chart: pixel width needed for a print by viewing distance and print width
Each cell is the width in pixels needed so that the pixels stop showing at the distance in its row, for the print width in its column. Read down to your viewing distance; the farther away, the fewer pixels.
| Print width | |||||
|---|---|---|---|---|---|
| Viewing distance | 12 in | 24 in | 36 in | 48 in | 60 in |
| 2 ft | 1,719 px | 3,438 px | 5,157 px | 6,875 px | 8,594 px |
| 4 ft | 859 px | 1,719 px | 2,578 px | 3,438 px | 4,297 px |
| 6 ft | 573 px | 1,146 px | 1,719 px | 2,292 px | 2,865 px |
| 10 ft | 344 px | 688 px | 1,031 px | 1,375 px | 1,719 px |
| 15 ft | 229 px | 458 px | 688 px | 917 px | 1,146 px |
Chart: resolution of a ten by eight inch print by the pixel size of the photo
Each cell is the pixels per inch on a ten by eight inch print for the photo width in its row and height in its column. The print is turned to match the photo, and the smaller of the two figures is shown because the photo must cover the sheet.
| Photo height in pixels | ||||
|---|---|---|---|---|
| Photo width in pixels | 1,600 px | 2,000 px | 3,000 px | 4,000 px |
| 2,400 px | 200 ppi | 240 ppi | 300 ppi | 300 ppi |
| 3,000 px | 200 ppi | 250 ppi | 300 ppi | 375 ppi |
| 4,000 px | 200 ppi | 250 ppi | 375 ppi | 400 ppi |
| 6,000 px | 200 ppi | 250 ppi | 375 ppi | 500 ppi |
Used by
- Photo print size from pixelsHow large a photo can be printed, from its pixel size.
- Pixels needed for a printThe pixel dimensions a photo needs for a print size.