What 300 DPI actually means
DPI is dots per inch: how many of the image's pixels land on each inch of paper. (Strictly, pixels per inch is PPI and dots per inch belongs to the printer, but everyone, print shops included, says DPI for both.)
It isn't a property of the image on its own. It depends on how big you print it. A photo of 2,400 × 3,000 pixels is 300 DPI at 8×10, 150 DPI at 16×20, and 100 DPI at 24×30. Same file, same pixels; the bigger the print, the thinner they're spread.
300 is the number for prints held in the hand, such as photos and cards, because the eye can't pick out individual pixels at that density up close. Prints seen from further away need less: 150 is plenty for a framed print on a wall, and banners need far less again (the large-format resolution guide has the numbers).
How many pixels you need at 300 DPI
| Print size (inches) | At 300 DPI | At 150 DPI |
|---|---|---|
| 4×6 | At 300 DPI: 1,200 × 1,800 | At 150 DPI: 600 × 900 |
| 5×7 | At 300 DPI: 1,500 × 2,100 | At 150 DPI: 750 × 1,050 |
| 8×10 | At 300 DPI: 2,400 × 3,000 | At 150 DPI: 1,200 × 1,500 |
| 11×14 | At 300 DPI: 3,300 × 4,200 | At 150 DPI: 1,650 × 2,100 |
| 16×20 | At 300 DPI: 4,800 × 6,000 | At 150 DPI: 2,400 × 3,000 |
| 18×24 | At 300 DPI: 5,400 × 7,200 | At 150 DPI: 2,700 × 3,600 |
| 24×36 | At 300 DPI: 7,200 × 10,800 | At 150 DPI: 3,600 × 5,400 |
To check your image, divide its width and height in pixels by 300. The result is the largest size, in inches, it prints at 300 DPI. The print size chart does this for every standard size.
Why a DPI converter doesn't fix it
Online DPI converters and the DPI box in most editors do one of two things, and neither makes a print sharper:
- Change the label only. The pixels stay exactly as they were and the file says 300 instead of 72. The print is identical, because the printer prints the pixels, not the label.
- Change the label and resample. The editor makes more pixels by averaging the ones you have. The file gets bigger, but it's a bigger copy of the same softness: no new detail is added.
If a print shop rejected the file as "not 300 DPI", relabelling it may get it past the check, and it will still print soft. What it needs is more real detail.
When changing the DPI setting is the right move
There is one case: the image already has enough pixels, but it's labelled 72 DPI, so print software opens it at the wrong physical size. A 7,200 × 10,800 poster labelled 72 DPI opens as a 100×150 inch canvas. Change the label without resampling:
- Photoshop: Image, then Image Size. Untick Resample, then set Resolution to 300.
- Mac Preview: Tools, then Adjust Size. Untick Resample image, then set Resolution to 300.
- GIMP (free): Image, then Print Size. Set X and Y resolution to 300.
The width and height in inches will change and the pixels will not. That is how you know it worked.
When the image doesn't have enough pixels
- 1
Find the original
Copies from texts, Facebook and screenshots are smaller than the photo that was taken. The original may already have enough pixels.
- 2
Print smaller
Divide the pixels by 300 and print at that size, or by 150 for something hung on a wall.
- 3
Upscale to the print size
An AI upscaler adds real detail, not averaged pixels. Resly takes the print size you type, delivers the pixels it needs, and the download is a PDF at the print size or a JPG or PNG already labelled to open at it. Output is capped at 16 megapixels, so very large prints come out below 300: a 16×20 is 3,577 × 4,472 pixels, about 224 DPI, which is sharp at wall-viewing distance.