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Image Resolution Explained Simply
Pixels, megapixels, DPI and PPI, and why the numbers on your camera do not mean what most people assume.
Pixels: the only measurement that always matters
Every digital image is a grid. Its resolution is simply how many columns and rows it has, written as width x height. A photo described as 3000 x 2000 has three thousand columns and two thousand rows.
This number is fixed at the moment the image is created. Everything else you will read below is derived from it.
Megapixels
Multiply width by height and you get the total pixel count. Divide by a million and you have megapixels. A 3000 x 2000 image is 6,000,000 pixels, or 6 MP.
Camera marketing leans heavily on this number, but it tells you less than it appears to. Doubling the megapixels does not double the detail; it increases each side by only about 40 percent. A 48 MP phone photo is not twice as detailed as a 24 MP one, and both are limited far more by the lens and the light than by the sensor's pixel count.
DPI and PPI
PPI means pixels per inch and DPI means dots per inch. Strictly, PPI describes an image and DPI describes a printer, but in everyday use people say DPI for both and no harm is done.
Here is what trips almost everyone up: the DPI value stored in a file changes nothing about the image. It is a note attached to the pixels saying what physical size they are intended to be. Change it from 72 to 300 in an editor and you have not added a single pixel; you have only changed the suggested print size.
A 3000 x 2000 image is 3000 x 2000 pixels whether it says 72 DPI or 300 DPI. At 300 DPI it will print 10 x 6.7 inches. At 72 DPI the same file will print 41 x 27 inches, and look far worse, because the same pixels are spread over more paper.
Screen resolution is a different thing entirely
When someone says their monitor is 1920 x 1080, they are describing the screen, not any image. A photograph displayed on that screen is scaled to fit, which is why the same picture can look sharp on a phone and soft on a large monitor: the phone packs far more pixels into each inch.
This is also why "72 DPI for web" is outdated advice. It came from old monitors and has not been meaningful for many years. For the web, what matters is the pixel dimensions and the file size.
Working out what you need
| Purpose | Sensible target |
|---|---|
| Social media post | 1080 to 1600 px on the long side |
| Website hero image | 1920 px wide |
| Marketplace product listing | 2000 px or more |
| 4 x 6 inch print | 1200 x 1800 |
| A4 print | 2480 x 3508 |
Why you cannot simply "increase the resolution"
People often ask an editor to raise an image to 300 DPI and expect it to improve. It cannot. The pixels that exist are all the information there is, and no setting creates more.
What you can do is generate plausible new pixels. Traditional enlargement does this by averaging, which looks soft. AI upscaling does it by prediction, using a model trained on millions of real images, which looks considerably better. Neither recovers information that was never captured, but the second produces a far more convincing result.
Quick reference
- Pixels are the real measurement. Everything else is derived.
- Megapixels are pixels divided by a million; a poor guide to quality.
- DPI in a file is a note about intended print size, nothing more.
- To print larger, you need more pixels, not a different DPI setting.
- To get more pixels, either start from a bigger original or upscale the image.