How to use this DPI calculator
- Enter the pixel width and height of your image. You will find these in the file's properties.
- Enter the size you want it printed at, and choose inches or centimetres.
- Read the horizontal and vertical DPI. Anything at or above 300 is print quality.
- Set a target DPI to see the pixel dimensions you would need for that print size.
- Check the maximum print size your current image supports at that target.
What this calculator shows
- Horizontal and vertical DPI separately, which reveals a stretched or mismatched aspect ratio.
- The exact pixel dimensions required to hit your target resolution.
- The largest print your existing image supports without dropping below the target.
- Instant recalculation as you type, with no button to press.
- Both inches and centimetres, since print suppliers use either.
- A plain verdict on whether the image is good enough to print at that size.
What DPI means and why it is confusing
DPI stands for dots per inch: how many dots of ink a printer lays down across one inch of paper. The closely related term PPI, pixels per inch, describes how many image pixels occupy that same inch. In everyday use the two are treated as interchangeable, and for this calculation they behave identically.
The crucial point is that DPI is not a property of your image file. An image has pixels, a fixed grid, say 3000 by 2000. DPI only comes into existence when you decide how large to print it. The same 3000-pixel-wide file is 300 DPI at ten inches wide and 100 DPI at thirty inches. Nothing about the file changed; only the physical size did.
The numbers that matter
- 300 DPI: the standard for photographic prints, magazines and anything held at reading distance.
- 150 DPI: acceptable for posters and material viewed from a metre or more away.
- 72 to 96 DPI: screen resolution, and far too low for print.
- Large-format banners: often printed at 30 to 100 DPI, because nobody stands close to a billboard.
Viewing distance is the hidden variable in all of this. A print you hold in your hand needs 300 DPI because your eye can resolve that detail at thirty centimetres. A banner seen from ten metres away does not, and printing one at 300 DPI would mean a file of absurd size for no visible benefit.
Working out what you need
The arithmetic is simple: pixels divided by inches gives DPI. To go the other way, multiply the print size in inches by your target DPI to get the pixels required. A 6 by 4 inch photograph at 300 DPI needs 1800 by 1200 pixels, comfortably within any modern phone camera.
An A4 page is 8.27 by 11.69 inches, so a full-bleed A4 print at 300 DPI requires roughly 2480 by 3508 pixels. That is why 300 DPI A4 is often described as needing about 8.7 megapixels, and why most phone photographs are perfectly adequate for it.
Why you cannot fix a low result by resizing
This is the mistake that costs people money at the print shop. Enlarging an image in editing software adds pixels by interpolation, inventing values between the ones that exist, so the DPI number rises while the actual detail does not. The print looks exactly as soft as it would have before, and sometimes worse for the added mush.
Changing the DPI field in image metadata is even more clearly cosmetic: it alters a note about intended print size and touches no pixels at all. The only genuine fixes are to obtain a higher-resolution original, print smaller, or accept the lower resolution because of the viewing distance. If the artwork is vector, export it at the exact size you need with the SVG converter, which redraws rather than interpolates.
Related measurements
To go the other way and convert between screen pixels and physical units directly, the pixels to inches converter and the centimetres to pixels converter handle those cases. If you need to change an image's actual dimensions rather than just calculate them, the image resizer does that with the aspect ratio locked.